I've been PCing inhouse for 13 years. I built an oven that would take rear end housings, motorcycle frames and anything in between. Also built 3 different roll-in racks that I hang stuff on where I PC them and then and then roll it into the oven.
I fabbed an angle iron frame, double sided with hotrolled sheetmetal (galvanized will give off toxic fumes), insulation in between, 32 X 32 X 65 tall. I used 2 convection oven elements in the bottom and incorporated an oven temp switch mounting the prob inside.
I really need to build one a little bigger as I can't bake bumpers in this size.