Well *Raises Hand* as a lvl 50 Fire/thorn and one of the only yes your right it is very End heavy and i face plant on several occasions :3 because of my lack of end; it is a very good farming build That being said from personal Experiences 
But if you are gonna continue with a fire/thorns i would get your butt working on "Farming" some moolah xD
or cash :3 cuz your gonna need it to slot properly xD especially at 50
and you wanna get your butt in gear xD by Hunting some accolades cuz i run out of end so fast and i need soem accolades to keep me alive x3
Currently i have the Accolades;
Accolades;
The Marshal Accolade +5 Max END ^^
Demonic Aura +(RES) All +50% But Psionic Attacks and +(DEF) All +50% But Psionic Attacks
Currently Working towards;
High Pain Threshold; Need to get all of the badges xD
Born in Battle; Need to take 10 Million points of damage loll xD
Well those r the main 4 i suggesst ou start getting at a higher level ro start workign towards now ^^ because i didnt and ive been regretting it for about 35 levells loll :3
Hope this helps 
Permadom will help with the end issues.
As another Level 50 Fire/Thorns I agree with Jim. It is a great Farming build. It is big damage and fast moving. Certainly endurance can be an issue. For that reason I chose to go with the Sirocco Patron Pool for Power Sink. In addition I have built quite a bit of recharge into the build to make domination available more frequently. Not Perma Dom but close. Between these two powers I always have a full bar of endurance waiting to happen.
ok i have a lvl 9 thorn dom but im not so sure how it would do if i farm with it. It has alot of cone and AoE attacks but it seems so endurance heavy evenwith stamina and how is it damage wise. plz help