Spray foam s great! Bought some of it with fire stop in it. Just be careful around the water lines, put in a little let it expand, then hit it again. Too much at one time, especially around the water lines will close the lines in some. I used some to seal a draft in a window frame once, it expanded so much the the window jammed close. The stuff is strong while expanding. In issue in rv, stops mice and air drafts around lines and cables. Area for outside shower was the worse area. Do No not forget the water heater area as well.
Marriot2 on Wheels 2017 Flagstaff Classic 832 OKBS
2013 GMC Denali 6.6L 2500 HD DMAX w\Alison Trans
Pepper Pomeranian rescue 101 days as camping buddy
Days camped in FR, 2011 = 20, 2012 = 57, 2013 = 59
... 2014 = 39, 2015 = 52, 2016 = 68, 3 more planned