If you are speaking of seams and the sealer used on a rubber roof to seal perforations in the roof, the generally accepted best product is probably DICOR. Easy to use and will hold for about two years. Using a dull flat blade, remove the old product and lay a nice bead of new product in its place. DICOR comes in a caulking tube type cylinder and is available at most any RV supply. It is the product of choice among most RV repair shops.
2003 Dodge HO 6 speed Laramie Dually, Jordan controller, RDS fuel tank, Air Ride 25K hitch
Carriage 36' fiver, Onan 6500, Prosine 2K inverter, 3 slides, MORyde IS and Kingpin