Insulation or mass for a cold frame?

I am building a cold frame out of brick. Would it be better to insulate the inside of the frame, or leave the insulation off to gain the thermal mass advantage?

well I'm about to build a cold frame too. My plan was to insulate the outside of the northern wall.
I found this article about building solar greenhouses very inspiring. My coldframe will be a miniature version of this greenhouse, but probably without the underground heat exchange system.

I think it would perform best if detailed like a passive solar home design. Include some thermal mass but put insulation to the outside of it.

And plan for a little extra room and stash some water in there, like 2 liter bottles, or gallon milk jugs. Stores more heat than masonary per pound and per volume (I think...).

troy