How is the best way to keep mice out of my boat

I don't remember where it was I read it, but I believe it was fabric softner sheets will work.  I believe they said to use softner sheets in all the areas a mouse would get to whilt it was coverd.  Might be worth a try.

Moth Balls, been using them for the last 4 years and they seem to work.

Well, they say rats will leave a sinking ship so maybe you ought to let the mice stay put.

The fabric softener sheets work for almost every animal but mice.  Moth balls have always worked and worked well for those little critters.

While in Florida I had problems with cats getting into the boat under the cover.  The moth balls did'n't bother the cats one bit, but the fabric softenr sheets booted them the first time I tired them.

I've used both moth balls and fabric softner sheets in the past.  I haven't had any trouble.  So I could say both have worked.  Moth balls will also keep snakes away, for what that's worth.  

I had a problem with cats once. I left my boat on my driveway for a few days while I was doing some remodeling in my garage. A pregnant cat had a litter of kittens in a coveyhole under the passenger console. Cute little black with blue eyed kittens. I left the boat in the driveway for a couple of weeks until they moved out.

If I ever have to leave it out again, I will definately remember the dryer sheets!

Put a CATfish in the livewell

Cobras work well.