This goes for SSPs and any other classic or collectible you may have. I have several other vehicles, including my SSP, and have a steel building with multiple rollup doors I keep them in. What I have been struggling with for 20 years is mice. No matter what I have tried to keep them out they always find a way in.
I have tried all sorts of spring traps, put bait out, tried ultrasonic noise generators and nothing works. I find mouse droppings in my vehs and my frustration level has grown.
I did find something, finally, that works. And that is the "Walk the Plank" mouse trap. There are many variations and you can easily find them online, but here is a link to a YT video for the one I bought and I can tell you it works fantastically:
https://www.youtube.com/watch?v=cITWGjeNPAM
You don't even need to put bait on it. Just water in the bucket attracts mice, especially in a closed area like my building and on hot days. They smell/sense the water and go for it all I have to do is dump out the water with their bodies and refill. In the last 2 months I have taken out 6 of them, while baited spring traps nearby sit unused and rotting. It's a war that will never be won, but I'm winning battles consistently. Perfect!