I've been in a mini-van full time for two years with no problems, until this year in Flagstaff AZ I got a mouse in my engine. Usually I'm the "live and let live" type, but I couldn't take the chance of chewed wires etc. I set out a mousetrap in cardboard ( so the mousetrap wouldn't fall into the engine) and got it the first night. Never had a problem after that. I've heard all kinds of ways to repel them, from leaving hood up at night, a light on inside the engine, or ammonia sprayed on the tires.
Spiders are a part of this life for sure, I can't be around toxic chemicals so that's out ... I just try not to bring them in lol! I brush my clothes off before going into the van if I've been under trees or another spidery place. I've had a few spiders in my van but nothing poisonous.
Scorpions, not likely they'll get in the van unless it's a hitchhiker, don't leave shoes outside, check for hitch-hikers on anything you're bringing back into the van.
The little insects are more aggravating ... flies, mosquitos, bees, knats ... make sure you have a good flyswatter lol!
~ Mary Ellen