Does the sub face need to be exposed?

I have a single Boston Pro 12.5 thats going in the back of my wagon. The wagon has a compartment in the far back floor with a hinged lid where there is storage and the spare tire is accessed. I have seen in similiar setups (wagons like mine) where they built a box (the 12.5 only needs 1cu ft sealed) and had it attached to this lid, with the sub facing up and exposed through the lid behind a grill. Obviously this makes the lid weigh a ton and its awkward when lifting it to access other items. What I was thinking of doing is building the box inside this compartment, then simply closing the lid on top of it so the sub/box doesn't need to be moved or lifted except if the spare is needed - then it would lift out as a separate component/"module". I know subs mount in trunks, so performance doesn't seem to suffer, but do I still need a space between the lid and sub box face for air to escape, etc.? I hope this makes sense - and thanks in advance for any help. Subtlety is EVERYTHING.

Thanks Dyohn......sounds like a good idea. Another reason I didn't want to attach it to the lid is because then I have to compensate the size of the box to insure it clears at an angle when the lid is opened. The bottom tier of the box actually fits inside the spare. Do you think auto carpeting is too thick a barrier? Was just wondering if I could still run carpet over the whole area (after a grill in installed) to help keep debris from getting through the grill and onto the sub face. Not sure if there is such a thing as acoustical carpet that breathes (like speaker cloth). Subtlety is EVERYTHING.