Another vote for 'Wunderseal" and yes indeed, you do need to lay it on very thick then stipple it to create a really rough 3D textured surface for maximum protection. It over-paints pretty well too if need be. Expect to dispose of any brushes you use to apply it! It dries very quickly when applying it so be warned - you can't hang about.
Rear arches in particular had lots of pretty bad star cracks after 20 years so when we had the car painted, I put a thick layer of Wunderseal under all the arches. No new damage seen in the last 10 years.
I had a spare unopened tin after doing the Westy in 2011 and unsurprisingly it had gone off a bit over the 10 years in between. I rescued it with some cellulose thinners. Added a bit more every so often and eventually it got soaked up to the point I was able to start stirring it. Got it back to full usable state and applied it to all the arches of the Midlana.