Well Dreams,
Your coach is so new that you probably don't think about these things, but I can tell you from experience that you should. None are all that expensive, but all are important.
Somebody mentioned to check the tire date codes. That is real important. It will also be a pain as they are usually between the duals. But along with that, you should suspect everything rubber and most of the plastic. Then there are other things that age out like coolant and brake fluid. And, buy a good grease gun. Grease is cheaper than parts.
About the propane tank, If it is bolted to the frame, it is an ASTM code tank. It is good until it rusts out. Just wire brush the ID plate (carefully) and spray a new coat of paint on it.
About that water leak, Winnies are a construction often (rudely) referred to as "Stick and Staple". The coach frame is pine 2x2 with the aluminum sheet stapled to it. If you have not been on the roof to look for any possible breaches, do so very soon. If you feel any soft places, save all your money your might spend on upgrades and use it for as long as it lasts. If you get a year more, you are luckier than many.
Matt