When you get a FWC at the factory, you get a manual (and manuals for all the appliances) and someone on the staff spends the time to give you a thorough run through on all the important things NOT to do with your camper. Since you are dealing with an owner who has only had it for a short time, you might not get a good run through. Here are some basics that I can think of:
1. When opening (popping up) the lid, MAKE SURE ALL THE LATCHES ARE OPEN! There are usually 6 latches that hold the lid down when you travel (2 rear, 2 side, 2 front). Forgetting the side latches can let you fold the lid when you pop it up which is no good. Also, make sure the latches are all closed when travelling. It is a little embarrassing to pull over on the highway when you realize that the front of your camper has popped up at 60mph. I imagine its worse than embarrassing if you don't catch it in time and hit something with it.
2. Make sure the water heater has water in it before turning it on. You should be able to check that the water heater has water in it by turning the sink all the way to hot and having water come out. Better yet, familiarize yourself with the water heater and open the blow off valve on the external side of the water heater. If their is pressurized water in the water heater, you should get water out of the blow off when you hold it open. Firing a dry water heater can fry it if it doesn't have working failsafes.
3. If driving with jacks attached (not recommended, but probably necessary in your situation), never forget they are there, as they stick out quite a bit and are prone to getting caught on rocks, posts, gas pumps etcetera, which will damage the camper.
4. Pay attention to amperage when plugging in to shore power. There should be labels on your shore power inlet telling you what you can and can't do.
5. If you take the camper off the truck so the camper is freestanding on jacks, you are not supposed to go in the camper as the floor is not designed to hold weight when it is not supported underneath. Many people build a pedestal or dolly platform so they can go in and out without it being on the truck.
6. Your camper must be winterized if it will be in sub-freezing temperatures with no heat on. This is the process where you make sure there is no water in the system, which can freeze and break pipes.
7. The roof is weak, and not meant to support weight. Do not walk on it, or store anything that exceeds the weight rating (100 pounds if I remember right). Clear snow off it like your life depends on it.
Quirks:
If your FWC has a regular 120v outlet (like in your house), most likely it will only work when you are plugged into shore power.
Condensation is a big issue with any camper. In cold weather when you are running the furnace inside, you will want to check under the mattress periodically for condensation. It will form there because it is a very exposed area with two moist humans sleeping on it, and condensation that forms on the canvas sides will run down and collect there. My wife and I actually slept and cooked in our FWC for a full year while we were building our house. This included a brutal winter. We had the thermal pack insulation in the canvas pop up, but we actually had to remove it so condensation on the canvas could dry. We also had to keep the under mattress condensation in check. We had actual ice beneath our mattress many times. A FWC camper is not designed for the winter, but it can be done.
Unloading and loading the camper on the truck for the first time can be difficult, and you will bicker with your spouse. Do not try and rush it or force anything. Watch a video about it, but also know that every rig has a little different geometry.