moth balls, just handle with care and make sure you air out the truck for days before use
i did that and it didnt keep them out but it kept me out and it still stinks in there after a year.
find any hole the size of a dime or larger and plug it any way you can. seal off where the steering column comes thru the firewall. now they're out. i hear dryer sheets are the ticket, i would try that before the mothballs. if they work or not you'll have a pleasant smell in the cab.
