I look at it this way..
something that ways 0.05dt should be quite easy to knock out if it's even only grazed -- thats' what I meant by 'vehicle' -- really just as justification for the tremendous amount of damage that a laser (or autocannon for that matter) would do to it.
And, actually, I think missiles could quite easily be designed as vehicles, and did so a while back as an experiment to see/show that the 6G rating was an arbitrary limit that didn't fit into existing rules. Missiles still have a high AC due to their tiny size and high agility, but all it takes is one hit.
The Torpedo idea is one I use -- this ways 1 ton and in game I treat it as a 1dt ship with a high AC due to size and agility.
Both have worked quite well in the encounters that i've run so far. In fact, my players are asking about putting autocannons on their ship as anti-missile weapons. I don't see why not, you throw a good deal of lead at something that is coming into you at at least 60G acceleration, and has been for a bit, it's speed alone puts enough KE into the small autocannon round that it'd destroy the missile.