I once owned a Safari motorhome and it had a vertical hand rail or grab mounted inside the vehicle at a point where it could be held onto when one was making the last step into the coach. Depending on the configuration of the trailer, one could be mounted fairly easily as long as you had a solid wall or cabinet back inside the door. You could install a wooden or aluminum plate inside the cabinet to strengthen it.
Placement would be up to the individual and subject to individual needs. You could either fashion one out of hardwood if you have any woodworking slills or purchase one designed for either the outside of an RV or for any number of uses - probably at Home Depot or Lowes.
Yes...I ordered the handrails (oak wood) actually from Forest River and when my Paradise Pointe was over in Topeka for warranty work, Randy put all 3 on...I have 2 doors...he put them as you go out, and I had one put going up to bedroom...I am a big guy and it did not make space any narrower.