OK, if you really want to keep the spiders and other bugs out of your truck, then do the following.
Skip the mothballs, essential lemon oil and drier sheets. Unless you want your truck to smell like a snuggly queer cedar chest.
Get Permethrin. Spray it on your carpets, seats, headliner - anything cloth. You'll need to check if it is OK for leather. It isn't like deet, so you don't have to worry about it melting plastics.
It is made from some flower - marigold, maybe? - and is not harmful to you once it dries, and isn't toxic when wet, just an irritant. It is made to be sprayed on clothes, tents, even mosquito netting. I've sprayed it on everything from BDUs to silk aloha shirts, and it has never stained anything. The effect lasts through a few washes on clothes, so it will probably last a long time in a truck. The stuff even works on sand fleas.
I like the spray bottle kind rather then the aerosol.