Go to a local do-it-yourself pest control store.
I bought some of this at one
http://www.amazon.com/Demon-Max-Inse...ords=Demon+Max
It's the same stuff the professional bug people use to spray houses, except "last year's model"....actually several years now....
The similar stuff I bought many years ago as a similar store was even better I think against some bugs, but I ran out of it and got this one a few years back....this one is rated for exterior application too, so it must have some level of resistance to water....
One bottle of this stuff will last you a long time...... I mix up a gallon every six months to a year or so and treat my whole house.
When I parked my RV a few months back, i sprayed the under sides, concentrating around the suspension components and frame members that a big might like to crawl on.... and inside around baseboards and in cabinets....