The stuff I use is the same vinyl lettering you'll see on cars, on walls in crafty homes, on windows, signs etc. I get it from my sister who has a machine that cuts out whatever she wants. It should be at any sign shop. I've even thought of buying a little vinyl cutting machine for around the shop (cricut) but I don't always use vinyl lettering, only for my personal amps and prototypes just to make them more presentable.
I've used it on powder coated steel chassis, hammer painted aluminum, powder coated aluminum and it never rubs off, moves or presents a problem. To me it seems like it would stick nicely on your chassis. I have also used this lettering on pedals which take abuse. The gray amp in my post above is silver hammer paint, it is not smooth but the lettering adheres to it.
As for painting...I struggled through this years ago and find that sanding the chassis lightly, wiping it clean with tack cloth, applying a coat of etching primer paint (bought at my local auto parts store) which preps the aluminum or steel chassis to adhere paint nicely. Then following with a couple coats of hammer paint or spray paint finalized with clear coat in either matte or gloss, depending on the look, works for me. I used to have problems with paint chipping off but not anymore.