Update time. Haven't made a ton of progress due to my job being crazy during the holidays, but have managed to do a bit.
I pulled all the branches out, and built the trunk out of 4" PVC, cork bark, foam, and rope. I cut about a dozen short lengths of PVC, and bent most of them with a heat gun. These will hold the branches at the trunk. This way, the branches are easy to replace, if needed, without disturbing much.
In order to try to avoid needing to replace the Ash branches, I sealed them all up with DryLock (tinted to light brown). Then, went back over them lightly with DryLock mixed with dark brown acrylic. There is one branch in there that is sealed with Titebond III instead, and one Ash branch that is plain -- so I can see how long they last with various treatments. I also filled it out some with manzanita.
Still lots to do with coating the structure, and the stand isn't painted yet either.
Current plan is to paint the exposed foam with the light brown DryLock, then go back with the dark brown DryLock to make it look more realistic. Planning to do vines above water with peat/silicone and vines below water with peat/Titebond III. Thoughts?
Sorry the flash makes the last two pictures look so washed out.