You can do long tubes in your oven
My first set, althouhg we used the Eastwood powder coat kit, the curing is same 425 for 20 minutes.
Simply make a template for the oven window, do one end at a time
It reallt does work & would be even easier if your just painting them
2nd set of long tubes we did come up with a better method,
Find that pizza place that has just gone under, best ovens in the world to cure powdercoat
warning - if the place happens to open up again, pass on pizza for the kids, at least more than once