Forest River makes an entry level product so the overall quality will be about average as TT's go. The very basic aluminum siding tells about the quality; minimal.
Ask to look at all maintenance/repair records.
Ask how old the tires are. If more then five years, they need to be replaced no matter how good they may appear. If the seller says they were replaced, ask to see the bill.
Tell the seller to turn on the ref. and hot water heater the day before you go to look. The ref. should be below 40* and the freezer close to 0*. Run the A/C and all other equipment when you're looking.
Especially, look closely at the ceiling for any signs of water stains.
Pressurize the water tank. If the pump runs when all faucets are closed, there is a leak.
Others will have more ideas.