Do yourself a favor and do it correctly.....remove the old caulk. It sucks, but you really should do it right.
Home Depot sells plastic caulk removal tools made by Hyde. You can find them where they sell the silicone.
Purchase some naphtha while your there. It cleans up the old residue and quickly drys.
Take your time and do a section at a time, once you get going, it goes quick.
Unfortunately, owning a truck camper ends up turning into a labor of love.
There is more info in: Camper Maintenance/ caulks, sealants-Roof replacements repairs,
found in the university.
Good Luck
Rick
2018 AF1140DB, 400W solar, Trimetric, Lifeline GPL-31XTโs, rear deck,
2019 5500 Ram Crew, DRW, 6.7L-CTD, Custom TC bed, on board air, Front Rack