Ur-Bantha
Bantha was the second Ur-spirit I came to agreement with on my own, and I believe that were it invoked in the name of the Biding Muskeg Clan it would not need to be renegotiated with. The Boon of the Bantha is one of persistence and stoicism. With it, you can tolerate cold, heat, sun and lack of food or water. Not forever of course, eventually you will weaken and die, this is what the web demands, but it will take much longer and you will be able to function much better than you would have otherwise. A being of Jedi training once compared it to tapas, and from their description, it is and isn't similar. Certainly the two could be used in the same circumstance, but from what I understood, tapas will alter the environment for you, even if it is only a thin layer over your skin. Say that you are freezing. Tapas will physically worm you. The Boon of the Bantha will make you able to tolerate the cold. It is you yourself who is affected. Tapas can however be used to survive vacuum, I would not suggest using this blessing for the same.

Ur-Vornskr
The Ur-Vornskr might answer the clans call, but I suspect any who wish the boon of this proud spirit will likely have to call upon it and make the first agreement themselves. I believe one of the keys to success in this is to show no fear, but to remain respectful. For the right to use it's gifts, I allowed the Ur-Vornskr to ride within my mind on a challenging hunt. I believe it would accept such a deal again. Warnings on that front. The hunt will need to end in a kill. Nothing less will placate the beast. To try and trick it is to invite calamity and bad luck upon both yourself and your allies. Secondly, while it will mostly be only a presence barely felt in your mind, understand that it is a predator, and an Ur-predator at that, know that you will be more aggressive, take this into account and remain in control. If this can be done, the Ur-Vornskr will grant its blessing easily enough. The Sense of the Vornskr allows you to track the force, as the beast itself does. It is possible to find non living but force imbued items, but this does take more concentration.