We use a similar product, rid-a-rat, under our hood. Haven't done a double-blind scientific test but it seems to work. Not sure how you'd use it inside the van compared to under the hood, which is a defined and enclosed area. There are some old threads about shining a bright light in the interior at night to find holes under the vehicle and blocking the holes.
We've picked up mice in our last two camps, which makes a total of three in 8 years. (Maybe a couple more than three.) Not sure why unless the drought and heat are making them hungrier. We may start setting traps over night.
We've also sprayed peppermint around the interior since it's supposed to be a deterrent. Didn't use it recently. May or may not help but it smells nice.
“Often bumpy roads lead to beautiful places. And this is a beautiful place.”
— Dave Martínez