For my explosive skill build i have:

4 piece HW with chest and backpack, 1 wyvern, 1 china light. Max or near max skill damage rolls on everything. Im hitting 2.7 mil seekers and 3.2 mil artillery turret. The 10 second cooldown talent on the pack does work but not the chest talent i don't think, but either way this setup hits harder than other combinations ive tried, basically get seekers back every 10 seconds, 13 seconds if i have to wait for the full turret cooldown, which is still not bad.

I use this build if there is a crit dps build in the group or if I'm running solo, it clears most challenging missions quickly if im alone. If you have a 4 man group and there's another skill build (cc or damage like this one) you will clear challenging no problem and with smart strategies can clear heroics pretty easily too, once you get comfortable with aiming the mortar turret.