you wouldn't have to seal the trunk. it all depends on how much you care about this potential project, or if you are just thinking it might be worth doing as an improvement over stock without obviously trying to win anyone over for SQ or SPL
essentially you'd be running the subs in an infinite baffle setup, meaning the "enclosure" (which the entire trunk would be acting as) is too large to provide any pressure cushion against the speaker cone. some subs can't handle an IB setup, and so you might put them in and find out that they go wonky without air pressure pushing back on them and seize up or something. or they might not blow, but might just sound like **** or have very low output.
the other issue though would be depth, at least on the sedan there isn't much room below the deck until the trunk spring and other **** gets in the way. so you'd have to use baffles or something to elevate the subs an inch or two above the deck.
I don't know how often you use your backseat for people, but you could easily build a box to put on the floor behind your front seats. hell depending on how shallow these subs are you might even be able to fit them directly under your seats. I've even seen boxes built that tuck up in the very front of the passenger footwell. not saying it's the ideal setup but doesn't sound like you're going for perfection either
