How to caulk your RV. Aluminum sided motor homes, trailers and 5th wheels are a bit harder to caulk then fiberglass sided units. After 15 years and trying 20+ different types of caulk quad max has become my favorite. I use to use dyco 20/20 but noticed it cracked after a year or so. I switched to Pro Flex caulk which seemed to last longer but didn't bond well unless the surface was super clean. After using quad for the past 3 years its my favorite caulk for aluminum and fiberglass siding