Chasmo, have you tried ilex skin protectant paste.
I've never actually used it myself to treat a diaper rash type butt burn, although I've experienced tremendous results when applied to the red raw, oozing and festering skin around the Stoma of my loop ileostomy prior to my j pouch.
Once the ilex paste was applied, within 3 days my skin erosion was completely healed and I continued to apply the ilex, purely as a precaution until my takedown surgery.