Sorry, I should of specified the plants I'm wanting to mount.
It's hard to say how large. I would guess in the 3 ft. range. I'm wanting some thing naturalistic. I have several large size orchids I want to mount and some seedling that will be big plants.... Three Den. speciosum, C. maxima, C. gaskelliana, C. jenmannii, two L. purpurata, E. brassavolae, and one other C. un-named. I'm sure I will have more soon!!!!
I just mounted a Den. fimbriatum on a cedar fence plank that I cut down to 14". Its 6" wide. I found this to be much cheaper than cedar shingles and looks about the same.
I'm not sure the cedar plank nor the cork would last with the weight that these plants will weight. I'm looking to get a decade of growth out of these mounts. I have one L. anceps mounted on apricot branch and several others mounted on manzanita branches.