Tall, wide and shallow box?

I've considered building a LLT for some time now. In a year or two I will start construction of my new house, and I'm planning on a serious build then, but in the meantime i'd like to get some building experience and try a few things out.

So, in the back of my room I have a double french door to my office. The office has another entrance, so the doors are pretty much just there to mess up my acoustics. I have a PB12+/2 behind my couch, and it works pretty well there. So I thought I might remove the door blades and build a big subwoofer instead, filling the hole in the wall. The opening is 150cm wide by 210cm tall. So if I make this box 40cm deep I'm getting some 1200l volume. I'm concerned about the shallow box, though. Will be great for looks and not using much floorspace, but will such a shallow box work at all?
I'm planning on using two rl-p15 and a behringer 2500, and maybe keeping my pb12+/2 if it's needed to even out the response.

Is this at all feasible? Any tips?