Advice on a 2005 TT that hasn't been moved in 13 yrs

I had mine in a seasonal site for its first year. The area was all trees. The roof took a breathing! I was up there almost every weekend cleaning it and removing sticks and branches. After that it was almost exclisively kept in indoor storage for the winters. I clean the roof once or twice a year. And check and reseal he caulking. If it’s never been touched I would be worried more about water and rodent damage. The brakes and bearings may be ok. Bearings will need to be cleaned and repacked at minimum and brakes inspected. Tires will for sure needle to be replaced. Hey may be ok to get you to the closest tire store.

Look look look, and inspect everything closely!

Consider hiring a mobile RV Tech to inspect the TT. Or, do you have a friend who RV's that could help you check out the unit?
A small leak can cause a lot of damage.

You should be concerned with the BRAKES/BEARINGS. Would need to tear into them and inspect.....easier to just replace with new

Tires....forget about them. They WILL need to be replaced

After that you would have a trailer that could be moved.....that would allow you to check it frame was twisted from improper support for past 13 yrs

Was roof/side wall chalking maintained or is it the same old original dried up chalking.
Any internal signs of water staining?
Any signs of external 'delamination'?

Do the appliances work?

ETC ETC ETC

My bet is it's going to be a "restoration project" once you start digging below the surface. Fine if you're wanting a project. Maybe not so fine if you actually want something you can travel with and use in the near term.

If you buy it have a pro move it directly to a RV tire/brake shop. IMO none of the items you listed will be working. “Looks really nice” and water tight?

Wheels and bearing would be the least of my worries.

Sitting that long, what's the roof material like. Has it been under full sun all those years?

Next concern, how many rodents built homes in the underbelly?