Hi Bfonner,
I know you asked about price and how to negotiate. Don't feel like you have to rush in. Take your time and find something you are comfortable with. Learn from this community - you'll find a lot of information and opinions that can be helpful.
You may want to consider learning about how to do a walkthrough so you know if the camper you are looking at is a good one. Even with the same brand and model, there can be big differences in how well built each unit is.
At some dealerships, you may find multiples of the one you want. Before starting to negotiate price, do a thorough inspection of the actual unit you are interested in. Does it seem well made? Is the caulk where it should be? Is there rust on any parts?
Price is also not the only consideration. Does the salesperson you are dealing with seem decent. Will you get support after the sale? Some RV salespeople and dealers are actually good to work with. Rather than a specific percentage discount, consider working with your salesperson to get to a mutually agreeable deal.
I tried to capture some of our RV shopping lessons learned in:
Seven RV Shopping Warning Signs Hope that helps.