Mount waterpproof treatment. Ideas please.

[bil]

OK, I was thinking. Branch mounts have a problem, The problem with the finer branch mounts is that they risk rot weakening them. Now, here is a question. Is there anything that I could paint onto a dried branch that would soak in, and form a strong, water proof seal, that would last for a good, long time? Like varnish, but really durable. It would obviously need to be non toxic, and be the sort of surface that roots could adhere to.

I wonder if the sort of varnish they put on seagoing wood boats would do the trick?

Any ideas?