Use Ballistas and Eyodins against the Troll Rider
Bring Ballistas and Eyodins to the first commander fight. The Troll Rider and its mount have high durability. Use placements that cover the trench route the pair will take so the towers can fire as they approach.
Check a Boltskot tile before you build
In the 0.19.4e demo, one opening Boltskot preview on a high tile above the trench showed 75 Wood and +1.2 Range. Check both the price and the range modifier in your preview before committing your Wood.
Compare a few tiles along the lane. The extra range is useful when it reaches more of the route or covers a part of the trench another tower cannot reach.