I have used this on a couple of areas that separated from the side of the trailer and it appears to be holding OK after 8-9 months. CW has it for about $15.95 but you can find it cheaper if you search on-line.
"Developed specifically for RV use, ProFlex Flexible RV Sealant is more elastic than silicone sealants, and has superior adhesion as well. Tripolymer formula displaces water that might be hiding in seams and joints, and ensures a watertight seal. Bonds to virtually every RV material, even when damp, oily or frozen. Long lasting durable and paintable. USA."</span>