I have done this on the box for my carvin head. I'm in the process of doing the same on my 1x18" cab and there are a few things that came up:
To keep goop out of the screw holes (and so you can find them again) I cut inch or so long sections of straws and stuck them in there. Fit like a charm. I also used a bent wire hanger to hold the box up on a clothes line while spraying, but I'm not sure if that would work with a heavy cab.
Make sure you strip every stinkin' thing off of that finish and sand it smooth. Not only will imperfections show, but if you leave a little piece of carpet fuzz, it gets covered in rubber then falls of.
Treat it just like paint. Prepare your area, spray with a mask (this stuff is SO BAD to breath in) and let it dry for as long as you can possibly stand, or at least what the can says. Be ready to have to leave it overnight to dry without smelling up the house.
Use a primer coat on the wood first, not just bed liner. It takes a lot of the stuff to get to actually start covering the wood with a usable thickness.
You will use A LOT of bed liner. I was using the spray cans you get at the hardware store, and I went through three before I got a thickness I was satisfied with... and that was only for that small box.
The way you spray it, particularly the distance from the wood, has a HUGE impact on the end result. If you stay close and let it sort of "pool up" and get thick, it dries smooth and looks a lot like Tolex. If you go farther away, more like when using regular spray paint, the rubber gets "particle-ish" and form a rough layer that can brush off if you don't let it dry right. It feels like sand is being brushed off the surface. (I plan on doing the former and letting it collect and go smooth when I do my 118.)
I remedied this in later step when I spray painted white over that layer. Two (maybe three... it's been a while since I did this) coats of that looked pretty good, so I didn't bother with a clear coat.
This was what I learned from painting the box for my Carvin BX1200 head. I did the box as experiment so I could screw that up instead of my cab, and now I can pass that knowledge on to you! I'm just surprised someone else wanted to do it. I wish I could tell you the effects it would have on the sound, but I'm still in the carpet stripping stage on my cab. I am an audio nerd, though, and my gut tells me it wouldn't
hurt the sound, but it would
change the sound. I'm guessing the low mid-range response might be changed... maybe... a little. I doubt any but the most discerning ears would hear it.
If you have any questions, feel free, and let us know how it works out.
