I have a number of small vandas like that doing very well in small plastic baskets with a little EpiWeb to stablilize them. Most of my vandas are hanging freely or in baskets and a few are mounted.
Hi, I have 2 vandas and they both are potted, and they seem to be doing well. I generally am not home during the day and from what I have read they like a lot a water and don't like to be watered at night. So my theory is that the medium will hold the water longer during the day when I am unable to mist or water. I don't know if this is right or wrong but it does seem to work for me. (right now anyway).
I have two Ascocendas that I've grown in Sphagnum for years inside the house. I waterd them twice a week by soaking them, sometimes overnight. One has bloomed consistantly year in an year out but I can honestly say that they have not thrived. I now have them in a greenhouse with better humidity and have removed the Sphagnum. They looked like they were doing better right up to day I sun burned them. I think they will survive but I pretty sure It will be a couple years before they look decent again.
Considering your location, humidity should not be a significant factor, so that tends to lead me toward very airy conditions, as in Susanne's situation.
Now you have to think about how frequently you want to water, and let that help you decide.
My greenhouse-grown vandaceous plants are all in various configurations of "airy" - bare root & hung from wires, in wooden baskets with no medium, wooden baskets of coarse charcoal or EpiWeb chunks, EpiWeb baskets, etc.