Ho ho ho,,, Very cool – –
I’v tried a few different types of putty’s over the years,,,,

Auto Spray Putty works well and gives a really nice finish ,,,,it takes way to many coats to get rid of the layer lines so sand the object smooth first then use it,,,,, and has a bit of flex to it

Timber putty works well and is easy to Sand down—but tends to crack if the part is flexed to much – I haven’t tried my Tamiya Putty which would be roughly the same as the Humbrol putty –($10 for a little tube) ?

Don’t even try Fiberglass Reinforced Auto Putty unless you like to sand with a Angle Grinder but it has best property’s – – ,

Normal 2 part Auto Putty is a bit easier to sand and the fumes are good too –,,when I was building Boat hulls for this guy he had some great fillers that had a fair but of Flex but I can’t remember their names ( I think it’s because of the Fumes) but they were expensive as hell,,

I sure there’s plenty of builders out there that have tried many different methods –,,