Ok, one more question and I promise to just get on with it and do it
If you're not adding the inline fuse and temp sensor is there any advantage to wiring it in parallel rather than hooking the new element up to the old one as TedEBear did?
It seems to me that this route would mean the new element is protected by the existing in-line first, the same as the old one. I'd assume that's not a good as a dedicated fuse for each but better than nothing... I'm useless at electrics though so happy to be corrected. Looks a lot simpler to do too of course 
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Hello wurzel,
I'm no electrical wizard either. I wired my second 500 watt element completely independent of the original one because I had a surplus of appropriate high temp wire and I felt that the factory wiring used to power the original element might not be sufficient to carry the current for the additional element.
For this reason I ran a wire from each end of the second element all the way back through rear panel and connected them directly to the power source where the original element wires get their power. If the wiring for the first element ever fails the second element will still work and vise versa.
As far as the thermal fuse; if you wire the unit like I did, each element should have one as each element has power available in an overheat situation. However, if you simply jump the second element off the terminals on the first element an overheat situation should interrupt power to both elements in an over heat situation.
Personally, I never leave my smoker unattended for more than an hour and even then I'm not far away. I know they are designed to be fully automatic and safe but I simply won't take the chance as people have had fires for various reasons including failures to load the smoker correctly or clean it properly.
Wire it either way and simply keep a reasonable eye on it is my advise.