Hey Alex,
Our dogs were small, miniature schnauzers so they did not up that much room.
If it gets below freezing there,just get a hard hose and tape a heat tape to it and then cover it with foam pipe insulation. And if it gets really cold for extended times cover your dump valves with tinfoil then tape heat tape on them also. This will keep your water line operating and you will be able to dump your tanks.
Leave your black tank (toilet) closed, until full. You can leave your grey tank open (shower and sink water) all time.
Good luck, I hope this all works for you.