which sub enclosure to build?

I am going to build one of the 2 boxes poorly drawn below. Boths boxes are able to be taken in and out of my crew cab pickup truck. I want to know which box will work better.

Box 1 - gives me more air space per woofer but i'm worried about sound cancelation. (2.2 ^3 per woofer)

Box 2 - gives me less air space per woofer but i've made these in the past and they work well.  (1.45^3 per woofer)

The speakers are old Protech's (I have 12 laying around in my garage) When I had these in walls like shown in box 2 in my other car, its loudest tone was at 56 hertz in a 1.1^3 per woofer, so they do work ok in a small box.

I think I would prefer box 1 because of the extra air space so that they will play lower but do you think they will cancel out?

I will be using 2 mono class D amps, can you explain why stereo is louder than mono, i'm curious because i've been out of this game for a long time nad I just got the itch again.

Also i'm wondering why to invert the speakers, is it to get more airspace in the box, or for someother reason?

Thanks for the response and i'll definitely give your idea a shot

Thanks man, you cleared it up good for me.

Anyone else have any opinions because I know there are some pretty knowledgable people on here. I'm even open to other box configurations but I want to use 4 - 15's in some way because I have them and because of my amp setup

Thanks again