The lifespan of the RV sealant depends on the number of times you have to use it. It is common sense that the more you use the sealant for roofs the more caulk gets lesser in size. If your RV sealant is branded then you may need it only two times a year for recaulking.
So, that it is not used many times and the caulk remains for you to use for a longer duration. As the caulk gets stick to the surface because of its adhesive nature wherever they are applied so they last long for several years.