Most trailers come with 2 propane tanks; either 20 pound or 30 pound so you need to figure 40 to 60 pounds of propane. I wouldn't drop back to one tank. The nice thing about two is that when one gets empty the regulator automatically switches to the other tank and turns the marker red so you know to get the empty one refilled or swapped out. If you only have one tank when you run out you're just out.
You'll have to get a battery which is about 60 pounds for a little group 24 and can go up from there.
I always kept some water in the tanks for using the toilet or washing hands along our travels. We would often stop at an attraction and eat lunch in the RV in the parking lot before going in. It was nice to have the water for that. Also, campground water is almost always chlorinated which is disgusting to drink. We carried our well water from home in the tank for drinking.
Unless you're going to pull the plug out of your water heater and drain it each time you'll at least be carrying 6 gallons in there, that's another 50 pounds.
You may just have to ask the dealer what they may have added. Awnings are some times dealer added. Maybe a second air conditioner or a couple TVs.
