Lazyman 
Did you put a moisture barrier underneath the concrete slab?  
I DID NOT PUT A BARRIER UNDER THE SLAB,    The website recommended painting all interior surfaces  black but I just lined the interior with heavy black construction plastic, including much of the floor.   I figure if there is moisture under the plastic I don't care.    The inside temp gets over 125 on a sunny day so it seems to be working out.

Albert