I think I'd go with what you already have. Getting adhesive off you might have to go with mineral spirits to get after it and then the alcohol to get the residue of the solvent off. A couple years ago , I noticed that the poly sheeting under my wheel wells was just stapled in place and thought, here's a spot for water migration through the floors if I ever seen one and had some leftover white eternabond tape from a previous TT. Wanna guess what I used to seal up those staples? Eternabond is good but not a give away, if you look at the price of the Flex Seal for how much you get/ $$ it's no give away either!
2016 Flagstaff 27VRL Emerald
2020 Silverado 2500HD CC 4X4 6.6L gas 3.73