Is your goal to save the jump seats?
You should be able to put a single 10 or 12 in that shaped box.
You may want to have the sub firing down towards the floor, this way nobody will think you have a sub in there, maybe just a tool storage area.
Drawback is you won't get to watch it bounce to the music, plus is it won't get dirt all over it.
With the design you have drawn, both subs will have to share air space in that chamber, unless you make the box tall enough to allow for two separate chambers. Figuring the internal volume of that enclosure won't be an easy task either.
The box should be built to the specs of the specific sub you're using. If you make the box too small, it could damage the sub.
Check out the specs of the subs you're going to get & see if you will have enough room to build a proper sized enclosure first.
You can have cheap subs in a box made for them & they'll sound 100% better than expensive subs in a crappy box.
The size of the sub won't affect the sound quality as much as the proper (or improper) enclosure (not to mention what a good amplifier will do).