Has anyone ever designed a Drop Tank Tender?
You're truly into non-starship territory for one of those ... because no real "need" for a jump drive. The entire operation is "local" for pickup and disbursement.
Ideally what you're going to want is a Fuel Tender that can contain (buffer) LOTS of fuel, however, that big ship is more like a logistics depot. The real workhorses are going to be the fuel shuttles that go wilderness skim unrefined fuel and haul it up to the Tender. The trick is, it's going to take them "a while" to transit the 100D from world to jump point ... and they can USE that transit time to refine fuel while en route! That way, the fuel shuttles skim unrefined fuel, but deliver refined fuel to the depot Tender so as to buffer the logistics load.
You then have ANOTHER set of small craft whose sole job is to runabout and retrieve dropped tanks so they can be brought back in, refurbished and refueled by the Tender depot. Contracts and billing for services all get run through the Tender depot.
Depending on the specifics of the star system and worlds within it (and the number of likely destinations outbound from it) you could wind up with a half-dozen (or more) Tender depot operations plying their trade within a star system at different commonly used jump points.
Basic idea is to keep the fuel depot Tender "on station" near a jump point and then use fuel shuttles to and small craft to do the "legwork" of skimming fuel for transport and recovering drop tanks after use. That then permits the depot Tender to negotiate with multiple outbound ships on a somewhat expedited basis.
After that, it's mainly a matter of choosing a few drop tank sizes to "standardize" on (20 and 50 sound reasonable for free traders and other low end merchant traffic) with a single ship simply "stacking" as many drop tanks as needed to meet their jump fuel quota.
Beyond that ... it's a question of financing, business model and logistics.
Note that this kind of operational scheme is EXTREMELY SIMILAR (although the details are slightly different) to how XBoats and Tenders ought to operate along the Express Network.