Life Caulk or the Boat life caulk, good idea I forgot to mention that brand, thanks.Both 4200 and 5200 have ripped gel coat off when I needed to remove, so pick your poison . I've started using life caulk or lifeseal after getting sick of doing gel coat repairs. Seems like caulk would be a good choice for your project too since you may be removing it AGAIN next winter hahhaha
The drain plug area is now a scared spot. No touchy by strangers.