I would wait until it's dark outside. Turn on the lights inside TT, put a lantern in storage bins and close doors. Any place that you see light escaping can be a route for insects/rodents. Also, make sure the furnace vents are covered, (make sure to uncover before using again).
I plug the holes with copper/steel wool that I've placed inside a plastic bag. The steel can make a rust stain if not in a bag. The mice can't chew thru metal.
Make sure to clean TT. No food,( even canned), soap, candles, firewood, etc. I don't use traps or poison, as they either have an attractant or require bait, which just attracts more mice.
I also use those electronic, sonic things. That requires the TT to have power.
I park over a concrete pad, avoid long grass/weeds/overhead trees, etc.
I don't bother with moth balls or dryer sheets.
I put rubber snakes under the trailer to give the mice a little scare.
The biggest things are to plug entrances, and remove any thing that will attract them-as mentioned above.
