Ooh, do we need a TBM to enable the detail boxing?
No, wait, they're there, just not visible in the techroom. As a side note, there is a small angle from which the inside of the fighterbay is visible from outside the ship.
No, a TBM isn't needed. If you use the hatty in game, then the bay and engines only disappear when you are too far out to notice. If you look at it from every weird angle in F3, then yeah the detail box will not draw and things will get funky.
The small angle you found is there, but if I move any polys out of the detail box and onto the main hull, the gain from detail boxing minimalizes.
No, a TBM isn't needed. If you use the hatty in game, which is it's whole purpouse anyways, then the engines and bsy disappear