My experience has been just the opposite. 14 years of driving on off base while I was in and I never was in a vehicle that was searched. Very rarely the gate securtiy guy would stop the car and check ID's. That happened more at Offutt AFB (the former SAC HQ) than anywhere else. When they did that everyone had to show ID upon entering. Took about an extra 5-10 seconds per car assuming everyone had their ID ready to go. It caused such a goat-f**k that it would only be done in off hours and only when a heightened risk was expected.

Generally, if you have what appears to be a valid base sticker, you're waved through. Some of the isolated entry points will oftentimes have more stringent inspection procedures in place because they deal with far fewer vehicles.