That's a good idea for those corner covers in the cab, perfect speaker boxes.

I have some work to do before I get to the box but plans are to remove just about everything. Behind the drivers side rear door, I'd cut the floor lowering about 5-6' for a shower/toilet. Next to that would be a cabnets for propane stove/sink with a window, then frig/microwave.

For added space I'm thinking about 2 pop ups. First cut out the roof to raise it another 1.5 to 2 feet for standing room. Second cut out the passenger side wall approx 4" by 6".

The wall would hinge at the bottom laying flat when opened, this would be enough room for the bed and raised be the backing of a couch. A tent would have to be made like the side pop out campers that would open up as the wall is lowered. Sorry for the poor quality graphics but attached is a drawing of this idea.