I always post this additional advice:
Also, try to negotiate an out the door price so they don't try to include BS fees when signing the papers.
Remember, you are not there to be friends with the sales person. Be stern and let them know you are willing to walk out.
Bring in printouts of other RV's for sale from other places. If they see you looking at them after coming back from talking to the manager, a deal will be made in your favor (from my experience).
It never hurts to ask for free add-ons such as them installing Max-Air vents etc.