Sealing up plumbing openings

[KYAirstream]

I wasn't sure where to place this post, so I hope this is an acceptable area. It does pertain to plumbing that comes from the water heater into the trailer, as well as plumbing from the fresh water tank to the pump.... what do people use to seal up the area where the plumbing passes through? Spray foam seems like one option. Any others?

[Splitrock]

My water heater is in the trailer. The fresh water tank is below the floor just to the rear of the entry door. There's a fill hose and hose to the pump from the tank. Nothing really to fill there. Maybe a wad of steel wool to make it harder for a mouse to get in there.

[KYAirstream]

I take it you have an electric water heater then?

[Splitrock]

Water heater is gas/electric.