If you remove the furnace air ducts you won't have any hot air distribution throughout the RV. If you NEVER need heat, that would be OK, if you use the furnace you'll have problems getting heat distribution.
If you want heat, you may be able to reroute the ducts to put the air out in RV someplace else. You'll still have heat, it just won't be as efficient.
You can not just cut them to get them out of your way and then have the hot air blowing into the compartment where they run. This could overheat the furnace and cause a fire problem. You'll have to vent them out into the main part of the RV prior to where you want to do your modifications.
Bill