The cure temperature for standard powder coat plastics is 350 to 400F and there are some high temps coatings, for exhaust systems etc, that require a 1000F cure (beyond the range of most home coaters who, like me, use a standard kitchen oven for curing). I use an FDA coat for the inner surfaces of a Comocafe or La Peppina to prevent corrosion and it seems a good approach so far.
So, I don't think that the LP boiler or group would exceed the 400F cure for a standard coat, which is fairly economical to do. There is always the possibility of some unforseen fault, generally the result of surface prepreparation leading to failure of the surface adhesion. To get the powder to stick to the chrome you generally profile the surface with abrasion one way or another and can pretreat with chemicals for a better adhesion. Block all the ports and openings to keep the powder on the outside, mask threads and bolt holes etc.
Rough or pitted surfaces need to be either heavily preprocessed by filling with metal filler but an possibly better approach is to use textured finishes if you have a lot of pitting.
Likely the hardest part of doing such a job is deciding what color to make it.