Thanks for all for the tips! I am thinking of caulking with Buff Vulken 116 Polyurethane Sealant. It had good reviews at HD online, but am checking amazon too. Will update once we seal it. Going to try to do bottom side as much as possible, as well as interior floor.
Tremco 10.1-oz. Buff Vulkem 116 Polyurethane Sealant-7103012 - The Home Depot