How do mice get into your trunk?: With malice and aforethought, and they bring the whole famdamily. Oceans Eleven, my friend and we are the Tropicana.
I have tried in vain to seal my farm equipment against the furry horde to no avail: They are relentless and artful, able to transport bushels of acorns through the eye of a needle, stocking their rodent condos with near abandon.
Be afraid, be very afraid.

When I redid my a/c, I took the flapper door off of the return air in the passenger footwell and a big pile of acorns (dozens and dozens) fell out. Now I actually have some air velocity at my dash vents.

I had a conversation once with an exterminator about protecting a car from mice while in storage. This was after we found mouse evidence in the rear, well sealed, speaker box of my wife's 300ZX. He indicated the mothball trick, as well as Downy sheets and those electronic ultrasonic things don't do a whole lot., believe it or not he said the mice build up a tolerance for the scent! As mentioned they can climb exceptionally well, can fit through spaces big enough for their head and have an incredible vertical leap. His suggestion was traps with bait around the perimeter of the storage area.

"How do mice get into the trunk"??
Well, sometimes the elephant takes a really deep breath..
Sorry guys. ;)
Les

The best thing I have found is to use Bounce fabric softner sheets. The mice can not stand the smell and won't go into an area were they are. The other benefit is they don't smell as bad as mothballs.

Heater Box/Valve = Mice's Secret Entrance.

I gave up trying to keep them out. I found they only go for the dark spaces. On my targa, I leave the top off, hood and trunk open in the winter. No more mice. I did find a dead one when I pulled my Alt.; laying on the cooling fins. You might want to pull yours to check that they haven't built a nest and causing you cooling "issues"......Also, if you set a trap, don't give up after you have caught one, they don't travel alone. I got 5 before they checked out.....

Too funny........

I bought my car from a gentleman in VA, and mice had set up shop in the front pan...They chewed a hole in the trunk carpet, made a little nest, and collected sunflower seeds....

When I had the 30K mile service done, the tech found sunflower seeds on top of the engine, back by the oil cooler...He revved the engine a couple of times, and sunflower seeds sprayed into the engine bay!

That little section in the front pan looked nice and cozy! :p