I can verify that the Reaper brush-on primer works great for the Mansions of Madness minis. I’ve been on a quest this year to paint all my base set and first two expansions.
For best results:
Wash with soap and a toothbrush.
If any minis are bent out of shape, put a pot of water on the stove, and heat until it’s just making bubbles. You want it a bit less than actually boiling. Maybe 200 degrees F. While you wait, put cold water in a bowl. Add a few ice cubes if you have them. Dunk the affected mini(s) in the hot water for a few moments. Somewhere around 30 seconds to a couple minutes. You will see the mini straighten out. They get kind of “floppy” at this stage. Carefully, remove from hot water (I use a set of chopsticks) and drop immediately into the cold/ice water to “set” the correct position. Let minis sit in cold water until completely cold and firm.
Let minis dry overnight.
Optionally, trim any obvious mold lines with a sharp Exacto knife. Do not cut yourself.
Brush on a coat of primer. It doesn’t have to be very thick. You will still see some of the plastic color underneath. Use the primer straight from the bottle — do not thin with water.
Let dry overnight.
Go mad trying to paint the horrors.
FYI, here is my attempt at these guys. http://forum.reapermini.com/index.php?/topic/84350-mansions-of-madness-megaproject/&tab=comments#comment-1785071
I didn’t show any photos of it, but I gave all the minis except the ghosts an undercoat of Brown Liner after I primed them. The dark undercoat gives an overall darker/muted look to the final paint job that I wanted for (most of) these minis.