I have repaired quite a few pop up trailers at my business up until December 2015. Over the years I saw some really good deals and a whole lot more very sad people who bought a dying horse. For $4800 you can pick up a brand new Jayco with very, very low monthly payments.
A 13 year old trailer is going to have problems with the up and down system and you should expect to spend $400.00 and up to have the system rebuilt. NHSTA rules say that any tire sitting on the shelf in any tire store that is 4 years old must be recycled. So, you will need to buy three new tires and replace the bearings. If your not uncomfortable with sleeping on someone else's cooties, go right ahead and use those old mattresses. The propane regulator, tank and adjoining hoses are trash. Dry rot sneaks up on every trailer. Using a sharp, thin blade knife or even a sharpened nail poke it into any thing that looks like wood. The walls and ceiling are most susceptible, especially under the front and back panels. If you find soft spots, you might want to apply for a home equity loan before you continue.