Plan on repeating the process in a year or two if just using "caulk." Far better to use either a 2-component rapid-cure silicone (NOT silicone caulk), or even a quality polyurethane. All with proper surface preparation, of course, and go with a minimum thickness of at least 3/8" above the foam backer rod, slightly recessed so not to get torn by snow shovels, etc.