Funny to see this old post revived! The structure was almost like Shem suggested, essentially a semi-pit structure built into a hillside.
So results. Everything grew pretty well, I had early flowering on rajapuri and orinoco, and the cav. groupcv.s were getting close. Rajapuri choked even under plastic, but got ripe fruit from orinoco. I got fruit up to about half size on papaya and jakfruit too. Then in 2011 we had some bad weather and I got 30"of rain in 2 days with associated land slides etc. During the clean up a mob of cattle got into the structure and returned it to a pile of spare parts. As it was assembled out of eucalyptus poles thinned from my forest it was no great loss, but a shame I didn't quite prove my experiment either way.
My real job is organic farming, so part of the experiment was to see if I could produce organic bananas for local market. I used no fertiliser or sprays etc, just water and grass clippings for mulch. If if had continued I would look at soil fertility more seriously. I was amazed at how healthy the banana foliage was, that deep-green look that I remember from my time growing bananas commercially in the Australian subtropics. Considering mine were on very poor soil with only mulch I assume the heat made the difference.
Since that time I have not done much with bananas, as I have grown and planted about 250,000 forest trees and starting planting more easy-grow hardy fruit like avocados, cherimoyas, citrus tamarillo.
Some pictures;
Mahoi
General scene
Orinoco fruit, with the biggest commercial banana I could find in local shop for comparison
