Going to the Zoo, Aviary, Library, Science Center, McDonalds does not require a tour permit. You should still plan who will drive and ask if they have the proper auto insurance. Make sure seat belts will be used and that each boy has a signed permission slip. You must have a tour permit for a Webelos overnighter that is not on council property. The tour permit is a deterrent for fraudulent claims.
Liability insurance covers being wrongly sued by a parent for negligence.
Your individual pack insurance covers personal injuries. Your own personal auto insurance covers your vehicle. A Tour Permit has no bearing on your BSA liability insurance coverage.