I have several mounted Tolumnias. Two are mounted on hard wood and one on cork. I used sphag sparingly as a pad on the hard wood in particular since they don't retain water. As the Tolumnia'a attached (you will see the little roots wind their way across the wood), I used tweezers and removed most of the sphag (which doesn't have a unlimited life span anyway). On the cork, I don't remember using any moisture retentive material, but was very careful to keep the cork itself moist as the plant was establishing.
I do have to watch that the hard wood mounted guys aren't too dry. I dunk the whole thing (wood and all) every two or three days and mist at least daily, in the hot summer even more often. Mine are outside in summer and indoors in the winter which means high humidity in summer and low in winter. So I watch them year round.
The cork and first wood mount have been going for about 2 years now and the second wood mount which has 3 plants had had 2 of them for 2 years and I just added the third. All the plants mounted 2 years ago are established, growing and have bloomed. As they mature on the mount, I expect even better displays
. I just hope to get the three mounted together to bloom at the same time!