Having the worst luck this season with finding Ubers, there when i found an razorplate early on i figured ill stick to that build:
Robs thorn guide (cant seem to place links in the post)
I follow everything it says here, the skills, paragorn board, the stats on the gear and today i found a doombringer. Still even with shouts up and potions i dont have more then 185hp.
Really would like to know whats missing. My gear is masterworked 9/12.
How many ranks of Imposing Presence did you manage to get on your armor?
He needs +2 (base) on hat, pants, and amulet for Thorns.
If you get 3x masterworked on all of them, it’s +18.
i have +2 on pants, still rolling for it on neck, but its already costs me over 200m 
I have 15 ranks of Imposing Presence for 132k hp
154k with challenging shout and 76k thorns.
Not running razorplate any more.
Decided I liked a normal chest piece with Imposing presence and tough as nails passives.
More HP and more thorns.
but razorplate has over 20K thorns, how can u have more thorns without it?
When i equipped doombrionger i only saw an increase of 20k hp in my build.
now at 220k HP.
Farming the mats for masterworking is a pain though. As in that the dungeon it self is super easy until u get to the end boss. If u then see bramble it takes well over 5min to kill him.
Because life is thorns.
1 point in Outburst passive and you get 20% of your extra life as thorns.
Replacing razorplate lets you have more life and then tempered imposing presence boosts that life by 6% per rank and if you temper tough of nails on your gear as well you get a further 3% per rank as extra thorns on top.
You do lose out on the razorplate chance to boost the damage but you get to choose a different aspect.
I went with dodging heals for 20% life it’s pretty fun though I don’t have a very good dodge change only 12.5%.
I’m more bash focused with stun than thorns build but if I stack antivenon and fortitude potions I have around 235k hp and 120k thorns.
I only have 2 tempers for tough as nails and no points in it.