I'd say that surfing low clouds in the mountains is my absolute favorite thing to do in FPV. However, I only feel comfortable doing it in areas I'm very familiar with because it's very easy to get disoriented while chasing those gaps and tunnels in the clouds. Having a properly configured and thoroughly tested GPS rescue setup is essential for safety. I captured this flight a while back with my GEPRC Vapor D5.
Fasten your seatbelt and enjoy the ride!
https://youtu.be/sLR2j0lKeks