I have another article coming out on Tuesday next week, exploring various ways to use the cold frame, and I do go into some options for keeping it warm in that article. If you have access to an electrical outlet outside near your cold frame, there are various ways you can use lights and heating cables to add a little extra warmth. A much more "low tech" (and cheaper!) option is to place several large stones or cement blocks, or gallon jugs of water, inside the cold frame. They absorb heat all day, and then give it off all night.
I really think my favorite feature of this frame design is how easy it is for one person to move and set-up, and take down for storage. It is wonderful to not have to depend on someone else's schedule to determine when we set it up and take it down!
Thanks for reading and commenting, Darius! I'd love to see pictures when you have yours finished! Though my mom has used a frame for years, this is my first year with one (never too old to start, eh?), so I know I'll learn a lot as I go, too!