I'm sorry, but I have no experience with only using adhesive on that rail. My suggestion would be to use Liquid Nails construction adhesive. If it were me, I would lay down masking tape on either side of the rail lengthwise so that when the Liquid Nails or whatever adhesive you use oozes out of the side, it goes onto the tape and helps make a cleaner line after you remove the tape. There's a few sealants that might do the trick but it's probably the same thing Fleetwood used in the first place that failed. With that much length, you will still have to work fast and a partner with another tube starting from the other end will make for a more successful time of it.
