I used the spray foam in a pressure can found at at Lowes, Walmart, Home Depot, Menards, etc. and filled any and every opening where wires or plumbing entered/exited thru the floor of the camper.
No hole = no open door for mice, insects, spiders or other crawly critters!!
As a side note, for winter preparation while the camper is stored, I toss about "Fresh Cab" packets thru the camper. NEVER had a mouse issue!
"Fresh Cab" is available at most farm/home stores, at Walmart, etc. Best stuff every found to keep rodents out and it's cheap .... one box of 4 packets for about $12.00