2 pack on a helmet is fine, i've done many of them. The heat is to cure the paint but it tends to make the fibres swell in fibreglass and could distort a polycarbonate helmet. I can paint a tank like that no problem, i had a bike painting business for years and painted 5 of Barry Sheenes GP bikes for his collection, Mick Doohans camo RZ500 that he restored a couple of years ago, Steve Galls YZ250a, Dave Tanners RN400, RH250, TM400 Cheney and Velocette as well as many others modern and vintage. I work as a mechanic now and just do a little painting on the side if anyone needs any tanks like that done. Cheers