Hello Silje, I have a very healthy modesta in an empty teak basket - no potting mix at all. I hang it vertically & the roots are all over & through the slats. It needs quite a bit of attention as regards watering, being generously misted twice daily. It produces such a lot of roots that a medium sized basket was necessary. I find sphagnum to be a nuisance in the long term, but I can't see why the neofinetia potting style would not work, especially if you had a hollow core instead of the usual solid ball. I would not have called this species "Modest" at all, it really is beautiful in full bloom. Such long spikes, & the plant itself is very attractive anyway. Just my opinion. I make sure that all my mounted plants, & those in baskets get a really good washing with plain water every month. That way I hope to prevent any salt or other toxic build up. A gentle but thorough shower does the trick.