One thing not mentioned yet but is of extreme importance is FINDING THE LEAK SOURCE. There is really only one totally effective way to do this; place positive pressure inside
the trailer and spray the outer shell with a soap solution.
The result will be bubbles at any leak point caused by air flowing from the inside of the trailer to the outside. Any other attempt, other than a verified visual point of water entry is just an excursive in futility in most cases.
Some RV dealers use a turbine based machine that uses a ceiling fan's frame as the entry for the air that will add pressure to the interior. Others have had some success using powerful leaf blowers sealed into a window opening to create the positive pressure. Either method will yield results that far exceed the hit and miss of trying to 'guess' where the leak is actually originating.