Most of the flat-floor RIBs have a well at the transom that can be used as a sump. I mounted a 360GPH pump, a switch and a sealed battery in a box. The pump output has a check valve added to reduce cycling, and it leads to a 90-degree thu-hull mounted into a hole at the top of the transom. A 14AH battery (or larger) will last at least a month unless you have unusual amounts of rain for several weeks (one rainy week no problem). I have been using this setup at least 10 years.