There is a thread about a guy using a leaf blower stuck through a window and then sealed tight. Basically any method you can figure out to increase the pressure inside the trailer about 1PSI greater than outside will work fine. then spraying soapy water over the entire trailer and mark each bubble you find. Leaks from lack of maintenance can be very hard to pinpoint. Water tends to travel a long way from the leak to where it appears. Guess you have now learned a hard lessor. Seal, seal, seal. As for the repairs part of your question. Depends. if your sure it is a minor problem, clean and paint might be all you need to do. If on the other hand it is more serious like most leaks tend to be, it may involve a lot of removing and replacing rotten or moldy wood. You will not have a clue until you fix the leak first then open the damaged area and inspect it.