It's fairly straightforward to convert a small freighter into a pocket carrier assuming 1) you design a fighter with the freighter's cargo bay dimensions in mind, and 2) accept a rather slow launch rate. Candidates for pocket carrier include the Subsidized Merchant (ideally suited for this role other than its limited jump range, and possibly a candidate for Q-ship carrier if constructed with four hardpoints instead of two, with the additions being pop turrets), the Subsidized Liner, the Far Trader, the X-boat Tender (already designed to carry craft and therefore able to accept a wider range of fighters rather than relying on tailored designs), the Corsair (same), and the Free Trader (with significant modification to add bay doors - most likely at the bottom of the ship - from which to launch fighters, but that would certainly surprise an attacker). The various Traveller Adventure freighters could also serve in this role. There are almost certainly other canon ships that could serve in the role, the best candidates having large cargo doors and being smallish.
Playing around with deck-plans, I found that the 130% rule out of CT Book 5, the one for ships of 1000 dT and over, works very well when fitting fighters to a ship that wasn't originally designed for them. Most times I ended up needing pretty close to 130% to give room for the fighter and for people to get into the bay and board the things, not to mention wastage when 10 dT fighters tried to get into a 46 dT bay.
The fighters I'm using are a 6 dT short-range provincial fighter and 10 dT long-range provincial fighter, the latter being long-range because it is equipped with a small craft cabin. The fighters are the same height as a shipping container and blockish in configuration for most efficient use of space. The addition of the cabin on the long-range fighter greatly eases the launch rate problem for ships posted to a specific system for long-term protection, since the fighters can remain on station for several days and need only return to the carrier periodically for maintenance and rest. They're designed under Book-5 rules so have a bit of armor, enough at TL13 to prevent criticals from the typical single-turret batteries (aside from energy weapons). The 6 dT version is a bit under 3 meters by 3.75 meters by 6.75 meters. The 10 dT version comes in two types: a bit under 3 meters by 3.75 meters by a bit under 12 meters, and a bit under 3 meters by 4.5 meters by 10 meters. They'd launch and recover under computer control to minimize the risk of damage, but their armor would likely prevent damage at recovery speed.
All fighters are 6G, use Model-1 computers in place of a bridge, and are armed with three missile launchers. They're at a bit of a disadvantage in comparison to the opponents with a bridge and computer, but their agility and numbers offset that to a certain degree. They are also fairly cheap and expendable: losing an MCr11 fighter to put a few million credits of damage to a pirate is worth it to the extent that the pirate must factor in those costs when judging whether an attack is worthwhile. Damage rules are rather generous to pilots: only 4 in 36 result in the loss of the crew, and if you add armor to eliminate those then the worst scenario is losing all your fuel or having your weapons stripped off. Missile storage is the basic 7 battery-rounds available to a triple-missile turret, after which they must break off to land and re-arm. All are single-seat fighters. All are made to TL13 standards to avoid the fighter itself becoming a prize for a lower tech polity sending out raiders to steal tech. The carriers themselves are careful to stay out of the battle since they're unarmored and vulnerable to maneuver drive hits.
Pocket carriers and their fighters are intended for the anti-piracy/anti-privateer role, in which opponents are likely to be ships under 1000 dT with computer support limited to Model/2 or /3. They are hopelessly outmatched by opponents with military-grade electronics; if facing an attack by such an opponent they'd either jump out, land and hide, or surrender themselves without a fight.
The nice thing about using a subsidy ship in this role is you can include language in the subsidy contract to make them subject to call-up for military need, which means the sector government largely doesn't need to support the ship between uses; it will be out earning most of the cost of its support.
Playing around with deck-plans, I found that the 130% rule out of CT Book 5, the one for ships of 1000 dT and over, works very well when fitting fighters to a ship that wasn't originally designed for them. Most times I ended up needing pretty close to 130% to give room for the fighter and for people to get into the bay and board the things, not to mention wastage when 10 dT fighters tried to get into a 46 dT bay.
The fighters I'm using are a 6 dT short-range provincial fighter and 10 dT long-range provincial fighter, the latter being long-range because it is equipped with a small craft cabin. The fighters are the same height as a shipping container and blockish in configuration for most efficient use of space. The addition of the cabin on the long-range fighter greatly eases the launch rate problem for ships posted to a specific system for long-term protection, since the fighters can remain on station for several days and need only return to the carrier periodically for maintenance and rest. They're designed under Book-5 rules so have a bit of armor, enough at TL13 to prevent criticals from the typical single-turret batteries (aside from energy weapons). The 6 dT version is a bit under 3 meters by 3.75 meters by 6.75 meters. The 10 dT version comes in two types: a bit under 3 meters by 3.75 meters by a bit under 12 meters, and a bit under 3 meters by 4.5 meters by 10 meters. They'd launch and recover under computer control to minimize the risk of damage, but their armor would likely prevent damage at recovery speed.
All fighters are 6G, use Model-1 computers in place of a bridge, and are armed with three missile launchers. They're at a bit of a disadvantage in comparison to the opponents with a bridge and computer, but their agility and numbers offset that to a certain degree. They are also fairly cheap and expendable: losing an MCr11 fighter to put a few million credits of damage to a pirate is worth it to the extent that the pirate must factor in those costs when judging whether an attack is worthwhile. Damage rules are rather generous to pilots: only 4 in 36 result in the loss of the crew, and if you add armor to eliminate those then the worst scenario is losing all your fuel or having your weapons stripped off. Missile storage is the basic 7 battery-rounds available to a triple-missile turret, after which they must break off to land and re-arm. All are single-seat fighters. All are made to TL13 standards to avoid the fighter itself becoming a prize for a lower tech polity sending out raiders to steal tech. The carriers themselves are careful to stay out of the battle since they're unarmored and vulnerable to maneuver drive hits.
Pocket carriers and their fighters are intended for the anti-piracy/anti-privateer role, in which opponents are likely to be ships under 1000 dT with computer support limited to Model/2 or /3. They are hopelessly outmatched by opponents with military-grade electronics; if facing an attack by such an opponent they'd either jump out, land and hide, or surrender themselves without a fight.
The nice thing about using a subsidy ship in this role is you can include language in the subsidy contract to make them subject to call-up for military need, which means the sector government largely doesn't need to support the ship between uses; it will be out earning most of the cost of its support.
