filling in the interior cab corners on AD cabs..

[MrDude_1]

how are you guys filling in the gap at the back corners of the cab?

my idea lastnight was to weld on an "extension" of the floor out to meet the outer cab wall.. but use flexible seam sealer to connect the gap to the wall. Im mostly worried about cab and floor flex making it pull the body and putting a wave in the outer panel... but i need to seal off my cab the rest of the way... (keep out noise, fumes, etc.. and keep the AC and heat inside)