This was my original homebrew cerakote oven. Pretty chintzy, but I baked a lot of stuff in it until I upgraded. It would handle a barreled action no problem. I scrounged parts and built it for about $30. The thing that makes me nervous about using a grill or whatever that has been used for cooking is all the oil/grease it may have on it. Currently I use a 40" Masterbuilt smoker that has never had anything greasy or oily in it. It works way, way, way better than the old way.
Spraying Cerakote is not hard. Finding a way to bake it is not very hard. The key to success is your prep work. Do it right and you will get good results. Try and do it half-way, and it is highly probably you will want to go eat some rat poison. I would never sand parts for Cerakote application. I am sure some folks have gotten away with it, and you might. But the possibility of failure is significant. For me it is blast only. Use 100-120 grit aluminum oxide or garnet. Be sure the media you use has not been used for blasting anything greasy (note rat poison comment above). De-grease really good. Blast. De-gas at 250+ for 30 minutes. If there is even a hint of oil, de-grease and de-gas again. Most times you can get by without the de-gas, but eventually you will have a part that needs it. Mostly those parts that really need de-gas are cast. Like on Savage bolt parts, I have had trouble, as well as a few other minor parts. Good barrel and action steel I have never had trouble.