Far cheaper than a high quality new pellet grill is an ATC and some gaskets for your WSM 18.5". I almost bought a new Rec Tec earlier this year. I had given up on my WSM 22.5" because even an ATC could not contain its temp swings, and like you, I was tired of chasing temps on long cooks. Instead, I refreshed and renewed my 22.5" wsm with gaskets, new dampers, new door and a lid hinge. Now that all of the leaks are plugged, my ATC can hold the temp constant. It is almost as easy as a pellet grill; only firing it up is more work.
My ATC is a Stoker (no longer selling new units, just parts), but BBQ Guru, Thermoworks, and others sell excellent ATCs. If you are an electronic DIY'er, you can even build a heatermeter yourself. The current generation ATCs let you monitor and control a WSM remotely so overnight cooks no longer need to wait for the weekend.
Time to refresh my WSM 18" "Classic" that I bought new in the year 2008. Question, where did you place the gaskets and what type of lid hinge? Also, did you also replace the Lid damper?
Yah, but if you do a search on Ace's web site, they don't have any Smokefires listed...not even "coming soon".