I just inspected my RV3b. The horizontal stabilizer end cap fiberglass fairings are riveted in place and not wanting to drill out the rivets, as well as damage the paint, removed the fairing piece around the vertical and horizontal stabilizer.
Using a standard size drill, was able to slightly open up the rear most tooling hole. It is 19" from from the tooling hole opening to the outboard hinge rivet holes needing inspection. My recently purchased Teslong borescope came with a 16' long extension for the camera, shorter would've been better. At the lens end of the Teslong, there is a screwed on ring that protects the threads for a few attachments that come with the unit. Removing the ring allows a slightly smaller hole for the camera to fit through.
I marked the flexible snake 19" from the camera end with a piece of tape.
It was easy enough to work the camera cable 19" into the tooling hole. The Teslong I ordered also has a second lower resolution camera lens aimed 90 degrees from the primary lens. I put a pen mark on the piece tape oriented approximately 90 to the side looking lens, making it easier to aim the lens.
Using the side looking lens, was able to inspect the rivets. Unfortunately, it appears there are two cracks. The next plan is figuring out how to clean around the rivets and double check if I am in fact seeing cracks. It is very doable on the RV3, to inspect from the inboard side of the horizontal stabilizer.