-High Knockback (>45%) WF, I also equip one on follower when solo.
-Nat's Legacy for Caltrops spam, vault spam, and SP:gloom spam (reflect mobs). Also removes need for preparation
Entangling Shot-Shock Collar: IMO, best synergy with High IAS and knockback on windforce, allows you to herd/position mobs where you want them.
Spike trap-Sticky Trap: Set it and forget it type skill. It's as if you added a periodic 404% aoe damage effect to your sentries. Great range.
Vault-Tumble: Mobility for positioning. Essential for effective herding.
Caltrops-Jagged Spikes: Cheap, discipline-based damage/slow. Litter the battlefield with them. Makes herding easier, keeps mobs in sentry range longer.
Sentry-Spitfire Turret: Set it and forget it type skill. Main damage dealer, (175% arrows + 80% rockets) x 3 with high IAS is significant.
Shadow Power-Gloom: A must for reflect mobs.
Custom Engineering: Allows for 3 turrets, 6 sticky traps. Increases turret and trap time to 1 minute, increases caltrops time to 12 seconds.
Archery: Self explanatory
Balistics: +50% dmg to sentry rockets. More/less open skill slot based on preference. Tactical advantage, cull of the weak, perfectionist, and numbing traps work fine depending on what you need.
Brief description of tactics:
Place sentry, vault up to mobs, pop a bunch of sticky traps on low hp mobs, run back towards sentry while placing as many caltrops as possible, set 2nd sentry near first, keep mobs in in front of sentries and in caltrops locations with entangling shot/knockback spam, place third sentry with other two. Reset caltrops, sticky traps, spam entangling shot as needed.
Just watch the sentries tear through groups of mobs with multiple sticky bombs. If only I had a larger pickup radius. This build does very well in higher mp levels and group play when you dont have godly stats.