Class C 6.0L Chevy Workhorse engine upgrade tips needed

Supercharger x2, is probably the only real deal for power.

What helped me and worked well enough,make it breathe better.
I added a K-N air filter and dual exhaust on 2 older GM small blocks .
It helped on hills when towing a 6k TT. 6k plus the truck was 12k or so, probably close to your MH weight.
Even better than that , my new 2016 5.3 GM seems to work well with the 6 spd tranny towing the 6k TT . IMO, the new tranny's were a good move.