When I bought my 2002 steel horse trailer I noticed a leak in the dressing room by the seam in the roof.  I asked around (before I knew of this site) and was told to use silicone cucking.  I when on the roof and peeled off the old cucking and roughed up the edge some with sand paer (once again a tip I was told to do) and put down new silicone cucking. 

I am just wondering if that was the right thing to do.  The dressing room is just unfinished but we want to ad insulation, paneling and a small A/C.  I just don't want to get a leak again after that and have to redo it.  someone else mentioned Tar Tape but noone at the store knew what i was talking about...