I'm also interested in using PEX for cooling for my container house. There's not much on the net about it. What's a good lightweight medium for pouring over PEX to make a sub floor? The more information at this stage of the game will be helpful.
Here's a primer.
Radiant Floor Heating and Cooling - GreenGarageWiki and about moisture control and a link to moisture modeling software from Oak Ridge Nat'l Labs and Germany's Fraunhofer Institute of Bauphysics toward the bottom of the page.
Moisture Control - GreenGarageWiki
Viega Heating & Cooling Design Manual (pdf | 19.92 MB) has a very good design manual that now includes cooling. It's under installation manuals. All 184 pages.