I have heard lots of people swear by the vermiculite/pearlite mix but I 
don't use anything close.  I just get standard greenhouse trays and put an inc
of stone at the bottom for drainage.  Then I put down a layer of mulch.  
Since there are large gaps in the mulch I put a layer of 50/50 peat sand 
down to level it off a bit.   I just plant the plants in the trays and they
grow like crazy.  Most are coming out of dormancy now and I don't even
think any of the pings need to be kept dry during dormancy.  My P. gypsicola
plants don't seem to care anyway :)  I grow them all under shop lights and 
most are varying shades of pink or dark green.  I wouldn't mind aquiring 
more of these fine plants and if anyone is interested in trading, please
write me at:
klmott2planetx.bloomu.edu
I previously had problems growing mexicans and this works very well for me.
If anything needs further clarification let me know and I hope this helps.
Take care & keep on growing,
-Tom-  & Krissy