Google storm window clips.

I think you also want to put a backing strip of gasket material or neoprene rubber to seal the air leaks.

Consider using the foam pads that you can buy for camping. These have enough give that you should get a good seal.
Cut them in 1/2 wide strips.These glue onto the inner rim of the opening where you will put the panel. I think you want to compress the strip by 1/8" inch.

Because the panel is more flexible than a storm sash you will need to put more clips on it. Probably one every 6-8 inches.

I would suggest scrounging a couple of double slider windows for short term vent control. The panels will be off during the summer, on during the winter, but in between you have days when you need venting for the afternoon, but not the morning.

You also may want to have vents in the peak area.

If you can automate a couple vents using those temp controlled gadgets from Lee Valley, your temps will be a lot mroe stable.