I like your build. Lot of work on this one to get the look you want and your do'ing a good job on it. As for any putty work I use MMD green Squadron Products. I start sanding with 150 grit get it smooth then add more to low areas as needed after the area is shaped the way I want,I sand it with 200 then 400 then primer. After primer I use 600 on the primer all wet sanding. Then I start painting it and wet sanding with 800 up to 1000,1200,1500 if needed for a mirror finish.