okay that is really good to know! thank you !
So far so good! I have found that it keeps in heat over night from the day time sun. It is pretty roomie and steady as we have had some strong wind lately. That is why I like the design, it hold well in wind because its up against the back wall of the outside the garage. So far I would recommend it. I plan on leaving it up all winter to support my plants and plan on using it to grow some seedlings in a few months. The plant stand it comes with is a tad flimsy but you get what you pay for I guess haha My zucchinis and cucumbers are doing well in there so I can imagine your squash should be fine! I am still working on a heating system, now sure if ill stick with my small space heater ( which is a energy eater) or figure something else out. Good Luck!
I'm in Scotland, so moderately cold in winter. Rarely gets below 25f. We've had a largish (2m x 4m) polytunnel for 3 winters now and have experimented with keeping it warm. Even when it reached high 70's during sunny days it would drop to pretty much the same as outside temps at night. HOWEVER, protection from wind and rain made all the difference and frosts never killed anything inside. But obviously it wasn't warm enough for heat loving plants. My point being - it's not raised temps that make the difference...seems to be more about protection from wind chill etc.
We find that putting fleece over the plants inside helps a lot (actually in terms of temps - we had loads of thermometers out there to test all the combos). We had to recover last year and purchased plastic that is supposed to retain more heat - and it does work. For actual heat generation we have a 'hotbin' composter - which has quite a small footprint. By moving that into our polytunnel it had the double benefit of keeping the composting going all year whilst releasing a bit of heat into the polytunnel at night - but honestly, it's barely measurable.
But the key thing that I'd stress is that in *our experience* heat escapes. You're essentially heating the outside air UNLESS you can add some layers of insulation.
My thinking now is that wires to heat the soil will be better. If you can keep the soil warm, when you cover the soil/plants with fleece at night you create a little microclimate.
Others may disagree, but in my experience attempting to heat the space inside a polytunnel is a waste of time and money. Insulation is your best bet - keep in what's generated during the day by the sun.