Good luck with the negotiations.
Before you get down to discussing price, do a thorough walk-through if you can. Identify the condition of the unit. Even a new one may have issues. You'll want to know about those and ensure they will be resolved before you take delivery.
As other have mentioned, try to get the best price possible as the first step. While times may be different, the 25% off MSRP has been done by others. RV show prices have often been in that ballpark.
Watch out for fees. There are some dealers that add on many extras. You shouldn't have to pay for things like a delivery walk-through.
Once you get to the lowest possible price, see if you can get items included. Some dealers will say that parts is a separate department and they won't add anything. Others may give you a gift card to go shopping for what you need. Consider if you want upgraded water and sewer hoses, a Maxxair vent installed, a surge protector from Progressive Industries or Hughes, any power adapters/dog bones, checks & blocks, a hitch lock, etc.
Find an RV essentials checklist online and consider what you'll need. If you can get any of it included in the deal, it's a bonus.
Happy shopping.