I had a nice grass strip for 17 years (plowed it up this spring). In that time, a lot of people used it, but without exception, everyone asked. The rules were, that no one used it if it was wet, so there would be no ruts, as it was mowed like a yard. There are liability problems. I only denied one person use of the strip, because he had never gotten a license, and I was concerned about his flying ability (liability).
If it were me, I would identify were those strips in the area of your destination are, get the owner's phone number from the state, or call the local airport, do some networking, to find out about strips-phone numbers and call them. Most people will say yes, but would appreciate being asked ahead of time. To me, not asking, would be no different than someone hunting on your ground without permission. We are all enthusiastic about flying, but in my opinion, there is a protocol to entering someones else's property. Steve