SUPREME BOX DAP Kwik Seal Plus 10.1 oz. White Premium Kitchen and Bath Siliconized Caulk - Pack of 2 (20.2 oz in Total)

A good brand name with a good product. I really like siliconized caulk. It just holds up better, and unlike pure silicone it is paintable. Check around because there are similar products for less out there, or is you need more than 2 you can probably save buying a case. These tubes fit a standard caulking gun.

Haven't used the second tube yet, but found the first to work great for sealing my mom's shower in her camper she stays in for work. It was leaking fairly badly at the base despite the camper being less than a year old and the dealer was being a bit of a pain about sending anyone to look at it, so just decided to fix it myself. Did the repair about a month ago and she has said she hasn't seen any water in the floor since then, excluding what she gets on it when she gets out of the shower.