I fixed my trailer last year. Here is a link on how I did it. RV.Net Open Roads Forum: Travel Trailers: I found and repaired my leak
One thing I did not mention in the post that I think is necessary now, is that after I used mineral spirits on the roof membrane, it left an oily residue. This needs to be cleaned off. I used simple green then I scrubbed the area with water and a washcloth. I made sure the roof was dry and residue free. I have also read, since then, that some people are using paint thinner instead of Mineral spirts. Either way make sure the membrane is oil free.
Also, They recommend using a roller on the eternabond to press it into the membrane. I didn't have one. I used a large deep socket from a ratchet set. It worked great.