I went to an all day seminar on deep winter greenhouses yesterday (a friend wants to build one). This link has some info including a video of part of a past presentation.
One interesting idea was to eliminate the perforated air tubes running throughout the rock bed that are used to deliver the hot air to store heat. Instead, the university presenter suggested having a big perforated tube in the rock bed at each end and just letting the air flow end to end through the rocks (sort of like we do in a hot air collector with plenums). He didn't know of anyone here that had tried that idea yet, however.