Good advice Tmax. Thanks for that. What type of filler do you use. I've tried filler for plastic model kits but sometimes the primer doesn't adhere to it. I've also tried filler for plastic bumpers on cars, but that damn stuff goes hard before I can apply it!
I use Tamiya modeling putty for small gaps, joins and imperfections. If I’m having to mod something that requires a lot of filler (like in my AR build) I’ll use Bondo (car panel filler). But no matter what putty/filler I use, the filler-primer paint remains the same and doesn’t seem to have any problems adhering to anything - “Dupli-Color Filler Primer”. But other brands should work fine too.