Just browsed through some of the comments. I have powder coated smaller parts and the process consist of getting the part to bare metal, in this case your frame. I would sandblast or chemical treat the frame before heating it to 850 degrees. After the part is stripped to bare metal i usually bake the bare metal for 15 minutes at 350 degrees, this helps get a clean surface to spray on and helps powder adhere a bit.
I shoot the powder on the part while it is still warm, powder the part until it is covered than stick it in a oven at 350-375 degrees for 25 minutes. I let it cure for a bit and it looks great every time.
Im not a metal expert but heating anything to 850 degrees thats not designed for it would warrant some caution.