Any hole through the skin of the trailer can be a leakage source. The wiring for a clearance light, rivets on a seam, a crack in a vent, sun damaged caulking, a loose antenna, shade attach fittings etc.

The problem often arises, when the actual leak is not located where the water is seen within the trailer. It can travel many feet and drip in an area where it's not actually leaking. The first thing is to visually inspect every seam and caulking on the roof. If it's five years or older, most of the caulking should be renewed and may be cracked, brittle or even missing.

The old should be removed and replaced with a good quality marine polyurethane caulk. Do not use a household silicone. Don't bother to just add new on top of the old. Recaulked properly, the trailer should remain watertight for many years.

There are also other products that can be used. A variety of sealant tapes are sold that are peel, press and stick. For larger areas on roofs that may be better painted, (rusty or a desire to reduce bare aluminum temps), the whole roof or large areas can be coated with elastomeric products. They are bright white, long lasting and waterproof very well.