DP Purchase Advice Needed

So we are looking at a new RV that checks all of our boxes. It is a 2016 Winnebago 38P. This model has a unique floorplan that we really like and the dealer has it for what we feel is an excellent price. No complaints there. The issue is that it has almost certainly been sitting on their lot for 12-18 months, if not more. As a newbie to the Class A world, what kind of maintenance issues should I bring up when negotiating the deal? I was planning on hitting them up for an oil change at the least, and they are going to get the tire date code for me. How concerned should I be about the tires, assuming they are not terribly old. The unit has 1300 miles on it.

Thanks for any help.

Jp