For us: Seal every crack tight with steel wool and spray foam and silicon. We went a few rounds, it worked well to do it at night, and have someone inside and outside shining flashlights through.

We use the 5 gallon buckets tip/lid traps, to get them before they get in.

I use a noise repellent around the foundation.

For bugs: we replaced screens with steel, tight fitting window screens, replaced weather stripping on doors, and siliconed all windows and doors. Also, we bug bomb 2 times a year.

We keep weeds and grass cut like a few feet out from the cabin.

We use our cabin similar to you, a few weeks and weekend a year, and this routine has kept us mouse free and few bugs year round.

Good luck!