I've been using BalsaRite for years. It greatly improves adhesion. I've never experienced problems with it under the finish, by just brushing it on.

Sometimes the fabric formula gets thick in the can. I thin it with lacquer thinner.

Lately, I've been using the film formula, even under fabric.

Saying this, however, I've never seen the need to use it with MonoKote. It simply doesn't need it, as MK's adhesive is fine by itself.

I apply both formulas with a brush.