Ian,
Permethrin is a spray or liquid. You soak or spray/saturate your gear, bedding, clothing, shoes, etc., and let it dry. The treatment lasts thru several washings (up to 30, depending on application and fabric type). The liquid when wet is toxic to cats. So take extra care that your cat is not exposed. Once dried, there is no issues.
It works! The treatment is so effective at keeping the creepy crawlies away, I treat all my stuff once or twice a year. I'll even spray down the carpet in the van.
It is available at most big stores. Walmart has a brand under the Sawyer Products label, next to the bug spray. Outdoor stores usually carry it also. Look in the bug spray aisle. Unlike DEET based products, permethrin wont harm your nylon fabrics. I treat my backpack, have for years.
A few years ago, I treated a hat, a shirt and a bandana prior to a paddling trip. The others folks on the trip were swarmed by biting flies. I noticed the flies, but they only approached me, then flew away. I was SOLD!!
I've seen ticks jump off!! They hate the stuff.
There are several companies selling permethrin. Either in a concentrate or direct application. Check the labels and see if its necessary to dilute the product and application techniques. Prices vary widely, store to store. $10-$20 will treat most of your gear for a few months. Cheap, IMO.