Did you ever see the movie Philadelphia with Tom Hanks and Denzel Washington? Washington's character said several times in the movie "explain it to me like I'm a 5 year old". Use that line a lot while you do the demo.
Don't be afraid to ask questions, even if you think they are stupid. There are usually lots of switches and levers throughout a camper. Not all of them are labeled. We have two switches in our camper that aren't labeled. Figured out one easily, the other took some hunting. Ask what they are and make sure they work. If a switch turns the outside speakers on, make sure they actually do that without having to change anything on the radio. If our radio's fade is set to front, the outside speakers will not output sound. The fade needs to be set to send sound to both front and rear (plays inside and outside) or just rear (plays outside).
You definitely should record the demo if you have the ability to. We had a great demo when we bought our Hybrid TT. The dealer took us to their campground (gave us 2 night stay) and showed us how everything worked. It was thorough and took a couple hours. When we bought our MH we knew a lot already and just went over the stuff that was unfamiliar to us, like the generator, slides, power awning, etc. The demo person isn't always the salesman. Make sure the demo person knows you are new to RVs and make sure they go over everything.
Good luck and congratulations!
-Michael