Hi guys,
I used to use crack fill or DAP but it does dry out and it will crack, I found out on a wing root joint one time. For about $12 to $14 depending on the markup for your particular auto parts vendor, pick up a tube of Auto Body Spot Filler, it comes in green, red or white depending on manufacturer and brand. Currently I am using a brand called Nitro-Stan Putty 9001. Its red, sands as easy as DAP is able to take a prime coat then when painted is as stable as the rest of the surface. It is easily thinned down with Testor's Liquid Cement so you can get it in the holey resin castings we sometimes get faced with and without thinning is suitable to use anywhere White and Green Squadron putty is used. Your money buys you a tube that holds a pound of material. I'm a pretty prolific builder and I bought my present tube in 1996. 7 years is not too bad for a tube of putty.