I'm looking into a temporary spring-use-only greenhouse, something like this one...

http://i26.photobucket.com/albums/c123/XSugar333/Garden%20and%20Pond/GreenHouse.jpg

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I'm in north Ohio, zone 5, typically we can't plant our flowers and veggies until the last of May, and sometimes the first week of June.

A greenhouse like the one above would work great for the daytime, but I'm worried about the temps at night, because it could still drop into the 40's and sometimes even a 30 here and there.

So I'm trying to come up with an inexpensive way to heat this type of greenhouse during the nights. I thought of an idea but I don't know if the idea is crap or if it would actually work, maybe someone here could chime in with opinions.

My goal is simply to get an earlier start on spring planting, and ultimately having a bit of a longer growing season.

I'm thinking I could use a large rubbermade container filled with water and place an aquarium heater in the tub. Could this work at all? Would it be sufficient enough to heat the cold air thru the night?