if you are going to get one, you will need to order it with the RV from everything I have read and from the last time I talked to a dealer about it.
There is blocking they install to support it, that is not there if you don't order it with. So they are very expensive or nearly impossible to do after the fact.
With that said, i have been able to live without one. I am able to jump on the roof of my truck to the roof of my slideout to the roof if I really need to get up there..
my $.02 worth,
Bryan
2006 RAM 3500 MegaCab w/Cummins Turbo Diesel
Mopar Exhaust Brake
2004 Dutchemen 31BK