Hi Otto
We have a Ultra lite that we tow with a Expedition, it weight 4200 lbs before we put anything in it and the truck is rated for 9000 lbs.
On the inside of your drivers door there may be a sticker telling you all of the limits, if not you will find it in your manual. Call a dealer with the VIN number if nothing else but you need to know your limits before you buy.
Next is how do you see yourself camping? At a campground where you hook up to electric, water and sewer or out in the middle of no where with no hook ups? Will you be fair weather campers or will you be dealing with freezing temps? Over night is fine but day in and day out is harder.
Size is another thing. We saw 13 footers that had a bath, kitchen, heat and AC and thought how cute. In our 25ft we have more room and don't have to make the dinette into a bed. Other things are larger too like fresh water and holding tanks as well as storage.
Not much real info, more like things to consider.