Sounds like ya wanna build a doghouse there, using scraps behind some Home Depot, Capn Joe, not anything precise. Warp-free those things definitely are not. Even heavy Garolite phenolic will warp
if not properly countertensioned. What Durst did in the old days was really clever and fancy: they
made the baseboard out of matched lumber-core strips, clad them front and back with formica, then
dadoed in a precision bronze strip diagonal in the backside to counter-pull any temp-induced warp
on the upper, replete with precise little adjustment pins to reset the tension - and that didn't work
either !! The "baseboard" on my 8x10 color enlarger was salvaged off a 22-ft long process camera.
It's a machined steel vac easel with a full set of registration pins. I added an adjustable masking frame. It won't warp. In fact, I can stand on the thing. But it weighs about 400 lbs.