When I painted my bus, I power washed it w/ phosphate detergent, such as TSP.
Then sanded w/ 220 grit, some use deglosser liquid.
Quick wash, then wipedown with lacquer thinner.
Then primed entire bus.
Then sprayed w/ compressor powered HVLP gun from harbor freight (purple)
You's be wise to use hardener in your paint. Many who roll-on say they wish they'd sprayed.
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