William,

If you go to coat the brush with the plastic handle stuff, first take very rough sandpaper and score up the finish a little so it will stick effectively. The first time I did this, the brush was brand new, and it started to peel off pretty quickly.

I stripped the handles of my brushes, and then used a spar varnish on them. That has worked out well so far, with no cracking of the varnish to report.

---Michael