my guess is that 12-18 inches or so of well draining material should be adequate. assuming that you have a south or west facing exposure plants like delopermum (ice plants), sedums and sempervivums, and "bath pink" dianthus might be worth a trial as sun and drought tolerant. "true" alpines like drabas and dionysias for example are probably not going to make it. some good websites/nurseries to try might include plant delights and high country gardens maybe even yucca do. good luck.

Hello,
You might check out Siskiyou Rare Plant Nursery - they sell alpines and have a section of their catalogue for "plants for heat and humidity"

Erik

Here is a link that might be useful: Siskiyou Rare Plant Nursery