Jim, Thanks for those details. Let me tell you a bit more about the conditions we see here in winter. I garden in USDA zone 8, sometimes zone 9, depending on the strength of El Nino-Southern Oscillations and where the Pacific Decadal Oscillation is its cycle, which now definitely is in the cooler wetter part of its cycle. During warm dry cycles & ENSOs, frost free winters are common. During cold wet, the present winter is typical, solid zone 8 to upper zone 7 weather. 85-100 inches of rain is typical, most of it falling in fall-spring, with cool dry summers. This is just above the Columbia River on the coast, in the Pacific Northwest. In the recent cold spell this winter & late fall, we saw temps to 18F here (actually 22 at my place, but I'm in a warmer spot than the official weather recording station), and our winds are routinely above 80 for several storms each winter. Last winter we had 3 storms in 3 days, with winds during the last two 120 mph plus. The anemometers all died in this area, so we don't know what the max winds were––the devices reached around 127 mph and blew away. My problem, or should I say dither factors, in deciding what to build, have more to do with excessive wet and very strong winds than with winter cold. So I envision my proposed cold frame primarily as a rain shelter, but one that needs sturdy construction so the glazing can be tied down/anchored/bolted in place in strong winds. I saved some polycarbonate twinwall glazing from a recent sunroom rebuild (not mine, unfortunately, but our rental place), so plan to use this, as it can take direct strikes from wind-blown branches and clams dropped by crows (did I mention the tidelands a few feet away?), which all hard surfaces, including cars, roofs, decks and roads, are subject to. I also know I'll be trying copper strips for slug and snail resistance. The dither factors that remain include: inside height when closed. Anchoring the panels, when open or closed, in the wind. How deep to set the gravel base for good drainage. So, your information helps me, though as you can see, I am still pondering, and would love to hear from others about their systems. I expect an alpine greenhouse is in my future, to deal with the above issues, glazed with something very sturdy. Thanks, Kathleen Near the mouth of the Columbia River on the Pacific Ocean, where today it was clear, sunny, and above 60F. Snowdrops and crocus are flowering in my garden.