I 'm no expert or anything close to being one. I think you have a sound plan. can i give you my 2 cents worth.

use the expanding foam insulation that comes in a can to fill the cracks. it exspands to somthing like 10 times it size . its easy and fast to use and dries faster than silicon. (homedepot)

i wouldn't use the drinking water as added sheidling.

where is the toilet vented to?

in the other forums we do the same thing. descibe our set ups and let the rest point out the holes so we can fix them. i like the squirrel cage it moves alot of air.