imo, either method is going to leave it very bare inside, kinda hard to coat inside and where the 2 halfs are welded togeather. It's gonna rust there when it get's wet.

Blasting the outside you really don't disturb much inside.

I do steam clean the whole thing inside and out before blasting them. So there's no grease inside. Cheap and fast, works good for me. It's a K member...