Tamiya Extra thin (works like proweld), some times I use 25-30 second gap filling CA glue.
I use Vallejo acrylic filler putty. It is a resin based filler and does not shrink, it dries as hard as the styrene and fast too. I also use 25-30 second gap filling ca glue with the kicker.
Try using Vallejo varnishes. I use them straight out of the bottle with embossing powders and they work real great.