Years back during an early spring trip, I heard what I determined to be acorns rolling around in the front vent system. When I turned up the heat, I even got to smell roasting acorns, Hmmm?
A few days after returning home I got a wiff of what I thought was garbage, it got worse each day. Thinking I had dead mice in the vent system/heater core, off came the dash, the overhead vents, etc... lots of acorns but no mice. The stink continued to grow, days later when I was at my wits end I noticed my Doberman sniffing the passenger side door column. When I opened the door & took a sniff near the vent in the pillar... WHOA!!!
The little bastards living in the vents had made a hasty retreat, like lemmings, from the blasting heat, thru the vent in the passenger door & down into the door pillar. They all became trapped there as they could not climb back up and out.
I used my shop vac to remove over a dozen of the dead decaying mice.
In washing out the mess with Lysol, I discovered that there is a removable plastic plug at the bottom of the pillar. Needless to say after the stink was finally washed out, I have left the plug out as a emergency exit for future rodent intruders.
I have found that sprinkling moth balls around the tires when the van is parked for extended periods keeps them at bay, as the easiest way to get inside is by climbing right up the tires (I've seen  the prints).

"I hate those meeces to pieces"

Jim King
86 Syncro Westy
(Terapn)