Well, I believe I finally have achieved a result I can be proud of. Photos following, starting from black epoxy all of the way through to the final spray of clearcoat in Wimbledon White.
The acrylic sanding block was ok but not great for these fenders as they have some real crowns on them. I only saw one grade of flex when I bought mine and I wasn't about to buy another. So I ended up ditching it as it was hitting metal.
What I found worked really nice was to take the 11" Durablock and just go gently in a cross-hatch pattern, taking special care not to chase any low spots out. I just let the sandpaper do the work and didn't press too hard. I filled the low spots and kept at it.
When I thought I had it, I sprayed high fill primer and repeated. The second time, things were almost straight but not quite. So I repeated a third time. I
still had a little filler to apply at this point but decided to call it quits and spray a sealer coat.
This took a LOT longer than I expected... about six part-time days for both fenders.
Almost forgot, I had to mount the fenders and line things up before applying the first round of filler. This included some careful work getting the gaps even.
Epoxy:
After first fill, still mounted:
Door gap worked out. I actually thought I was close to done here.
The fenders had other plans for me. This one had received a few bumps in the 13 years I had her, but bringing it down to metal revealed that it had far more than I expected. This took a lot of minor bump and fill to get evened out.
I didn't take any photos of primer but it was pretty clear at this point that the end result was going to be a light year ahead of my earlier panels. There was not a ripple or bump to be found anywhere, even with a bright LED flashlight held just over the surface.
After clearcoat (no cut and buff yet). No runs anywhere.
Pretty happy with this. Definitely a show finish