GTP Rotor pack
I think you'd just be better off buying a GTP rotor pack off ebay with coated rotors. Seems like they were around $400. In all honesty, you're not likely to pick up more than 10-20HP or so (probably less) and the coating will eventually start to peel. Or you could just pick up a used 94/95 model blower.
Biggest problem with trying to use urethane, etc to coat yourself is inability to control the thickness of the coating, which is critical. Glisten PC, which is a top urethane coating from POR15, is supposed to settle down to a uniform thickness. But in practice, it sets a little too quickly and will have thick/thin spots.
If you can find it, VHT Motor bright is a nothing but a clear urethane suspended in acetone and toluene in rattle cans. Even in a spray it's difficult to get an even, consistant coating.
Daspanka