Sorry, I disagree with the dump the leaky trailer responses. Present construction techniques in the RV industry leaves too much room for failure. The Caulking used, is in itself timely and will eventually fail. And that's any RV. Likewise, the seals in slideouts, roof vents and windows can fail as well.
Since '85, when I first started RV'ing, construction methods have greatly improved but are not flawless, ie; Windows are now sealed from the inside instead of the reverse, which exposed screws to the elements. Rubber roofs replaced galvanized roofs that flexed against the seals, causing them to crack. Once the skin is cut for any opening, such as roof vents, doors, and windows, even an airstream made of aluminum will eventually leak through those seals. Quality made trailers just take longer than others. So, the older the unit, the more wear and tear will set in and the more prone the trailer will be to leaks.
The trick is to catch the problem early, not to dump an otherwise good deal on the trailer. Hence, the need for all of us to check the RV when in long term storage.
I would bring it to a qualified RV center and have it professionaly checked out. Or check every seal and the caulking all around the rig and roof for obvious cracks or missing sealant. If you have a slideout, run a hose over the top to see if any water enters the trailer at that point. Also, turn faucets on and check all plumbing for leaks. Don't forget the outside shower if you have one. LOL
Good advice also, but still.... not my PERSONAL preference ......
We tow our camper in D at all times. We just don't "gas on it!' when going up mountains (for example). We just take it easy, no sense in revving the motor up for no reason to get somewhere 5 minutes quicker overall. We tow with a 2000 F150, and our camper is about 4400 lbs. Plenty of motor, and tranny, no sense to waste the additional gas by dropping down to a lower gear..... unless we are going DOWNhill, then sometimes (like Old Fort Mtn.) we will shift down to 2nd and let the truck hold back the camper and save the brakes...
Well.... my wife can hook-up, drive/tow, and unhook without ANY assistance from me whatsoever! It pays to be married to a redneck girl lol.... Sometimes just to humor myself I play dumb and ask her if I'm doing something right/wrong just to see if she knows, and every time she is dead on the money with her answer.
Not to mention she can drive anything, back anything, etc.... I am just a lucky guy I guess LOL!
Hillbilly Camping at it's best!