passive solar heater using rocks

I've been collecting big rocks (but not too big to lift) for a rms I want to build sometime this summer, so I've got enough rocks to make a couple rms's, so I'm wondering if I could use the extra rocks to make a passive solar heater shown in the picture (if I can upload it)...
Anyway, the cabin is on a hill sloping downward to the south. My idea is to insulate the ground under the cabin, build a double pane plexiglass window facing South and put rocks in it so they absorb the solar rays in the daytime and radiate the heat into the cabin threw a
grate on the floor. The grate will also probably be removable so I can get under the cabin as the out side will be sealed off. Just wondering if it would work. I see a lot of active/passive solar projects over on builditsolar. A lot of good info and docs on other peoples
projects.

Hey Dan;
I think that will work just fine for you.
A few thoughts for you.  
Insulate everything but the grate area. Walls, floor and  ceiling.
Build an insulated drop in cover to replace your grate during winter days with no sun.


It could be a cold but not frozen storage room during the darkest part of winter...