I run Vorpal + Lostmauth with very low defensive status and i can do all solos without die as a trapper. I think you should try go less defensive, it works very well. Btw Lostmauth dont add much dmg to HRs since it only proc on the first tick of the powers, while for the other classes it procs on all ticks.
Im lvl 70, i get the Common Cause quest that send me to Mythral Mines or any other lair, but dont receive the Mythral Mines quest, so i cant enter in the lair.