So your staghorn is in a (probably cedar) basket with only sphagnum moss, correct? I would not grow a staghorn in sphagnum, though I do use it as a backing when mounting a small plant. That being said, if your plant has been growing this way for a year, and it does appear very healthy, you have gotten away with this medium because of the slatted basket.
Stags can be mounted on practically anything. I would not used treated lumber though. The absolutely best mounting material I have ever found is natural Portuguese cork. The cork has so many "toe-holds", does not retain any water, and is light as a feather. As your staghorn gets older and larger, it will really start to get heavy. All my really large (4 + years old) stags are on cork. They might have begun their life on other mounts but finally get moved to cork. Cork is pretty expensive but might last a life-time, so you get a lot of bang for the buck.
Another plant that seems to grow best on cork is the orchid. The orchid roots (orchid is an epiphyte, just like the staghorn) simply go crazy when mounted on cork. You can tell how happy an orchid plant is by its roots. Orchids are my true "passion".
