I stopped using hobby specific stuff a while ago. I tried the same stuff you use and hated it. I started using bondo glazing and spot putty not too long ago and havent looked back. Goes on easy, sands easy, doesnt shrink and it bonds to the plastic. I recomend wet sanding it though, the dust smells bad. A tube is $8 or so at the local auto parts store but last a long time. I recomend!