Used to do all my pushbike frames with Japlac, really good stuff with time patience and many coats.
Smooth Hammerite works well, but if spraying make sure you have plenty and I mean plenty of ventilation and a mask! I thought once that I would spray a VW Beetle with the original stuff!!!!!!!!!!!!!!!
Oh boy!!!!!!!!!!!!!!!!!!! After 10 minutes in the garage with the doors shut and the heat cranked up, I was unable to focus my eyes or orientate, my head had a wardrobe in it and I couldn't string a sentence together! Nothings changed there! Managed to get out of the garage and next day finished the job with a brush panel by panel. Lasted really well until I was front ended by a myopic Dundonian out for a toddle, but that's another story and I'm still bitter and twisted about it 20 years on.
Have fun, Bill