More often than not "peeling" paint is a prep issue. You said you "washed" before painting -with what? After a soapy water wash, I'll hit it with ospho, wait 24 hours, wipe it down with a good degreaser then paint.
Clarification: the oshpo preps the bare metal or lightly rusty metal like a good etching primer, one of those will work just as well.
Weber 26.75 OTG w/CI grates & SJ/WSM Mini
Home built 24"x72" reverse flow stick burner trailer with 18"x44" grill w/CI grates and upright SS gas oven/smoker.
Home built 48" fire pit with a 30"x30" Santa Maria style ranch grill.
Home built lump charcoal retort, iGrill & a bunch of other cooking toys.