They don't make high temp primer. If you talk to any professional paint shop they will tell you to make sure the metal is clean and use only high temp paint, no primer. I have painted many a smoker with just high temp paint and had no problems.
Green UDS (UGD)
Blue UDS (UBD)
Homemade 18"/36" Grillzilla
Lang 60, (RIP)
Home Built Trailer (500gallon Oil drum).(RIP)