On Thursday, August 1, 2019 at 4:26:22 PM UTC-7, wrote:
...I know, and have used Bondo to that depth on other things, but aircraft?
Thank you for the insight and expertise you have shown in the answers you have give.

There are a variety of fillers you can use. I'd suggest a mix of glass microballoons and laminating epoxy resin. Before you start the actual work, make a few test batches of filler to see how dry you can mix it before it does not spread properly. You want it as dry and light as you can practically work.

You'll want to sand the wing somewhere around 120 to 220 grit before applying filler to get a good bonding surface. Degrease the surface before applying filler with acetone to rid it of contaminants.

One common technique is to use your templates to cast in place a series of raised ribs of microballoons. Then apply and sand your filler between the raised ribs.

--Bob K.