I was faced with a problem of needing to keep my seeded pots under plastic but not allowed to put in a proper cold frame and/or greenhouse.
My solution was rather unusual but it worked well enough.
I bought 3 old wooden kitchen chairs ( without arms) at a second hand shop for $3 each. Set them up in a row, side by sides touching. in a level sunny spot and used the seats to hold my plastic flats loaded with seeded pots. I covered the chair seats with plastic so as not to rot out the wood. Then, I covered the entire array with heavy clear plastic and used clothes pins to hold the plastic around the legs of the chairs. The chairs backs kept the plastic well off my loaded flats at an nice angle and since they were off the cold earth below and could warm up quickly, germination was fast! I managed to start an entire garden's worth of vegies ( even pepper and tomato plants) and flowers this way and then simply folded up the plastic and stored the chairs for the following season.
The cost was under $20 and I could take it all with me if I had to move. Awesome.
That's a good idea! I made mine using a planter window I pulled out of a house that was about to be demolished and a second one out of an old swamp cooler stand. I found I still had to add heat though (oops! sorry seedlings!). There's my wife's 1200W room heater under the plastic tarp (I gave her an extra blanket) and a 500W halogen in the window. When it got hot on sunny days I just opened the window.