My crystal ball says that Workhorse will refer you to the RV manufacturer (LaPalma). The limiting factor on the tonque weight is the frame extension that was added by LaPalma. It is unlikely that LaPalma will be amenable to raising the tonque weight, but miracles do happen.
As discussed in other threads, you will need to find a local shop that has the knowledge and skills to reinforce the frame extension to handle the additional load.
2002 35R Southwind, W22 8.1L Vortec UltraPower, 19.5' wheels
Toad: Wrangler, lifted and on 35" tires