I use only grapevine. I mount thousands using about 200 pounds of grapevine a month.
Grapevine as you found is very beautiful and hard. It has a life span of 10-15 years as opposed to pine (2-3 years).
Cattleys will atach their roots easily as well as dens. Oncidiums always need support. Do not be concerned. Tie it on and let it grow as it wants.
This one is a 30 inch plant on about a 20 inch piece of grapevine. You do not see the fishing line holding the plant which is around the sphag. the little line is
green plastic coated wire (bonsai traing wire) used to support the extra weight.
This mount is about a 28 inch piece of grapevine with multiple plants
