You have the enclosed underbelly option. I would not say it will keep out rodents. I would spend some time under the unit and located every tiny crack, and fill it with a brass wool material (pot scrubby) and then marine silicone caulk. I do not recommend spray foam. Two reasons, one over time is absorbs water. 1st; Water + campers = rot. Second; it is very messy to use especially upside down while crawling under the trailer, you will have a lot on you and the driveway.