Depends on the labeling method you go for.
When I tried water slides, I used laser ones in the hope they would withstand the heat, but I found they either went slightly brown on the lighter enclosures, of cracked under the powder coat clear. I've never tried envirotex so I can't comment on that.
I did have a few good results using a toner transfer technique that Davent showed me. Printing something on paper using a laser printer, brushing some clear acrylic medium on using a brush, then pressing the toner down into it. When it's dry, rub the paper off with water, and clear up the excess medium. I powder coated clear over it, and after a few goes, had a couple of really good looking boxes.
If you do mess any boxes up (I've messed up loads), soak them in acetone for 30 mins and then the powder coat will wipe off them. I've threw away loads of boxes before I realised this!
