At the top you can see last year's winter radiator block. I made it out of a pizza box lid according to a template that a member of Insight Central posted. But pizza box lids aren't very durable, and it needed to be retired, so this year I made a couple out of coroplast. You only need one, I'll probably donate the extra one to someone else.
This is where it goes in the car. It fits nice and snug. I don't know if it can easily be attached to an Insight w/o AC, but on ones with AC like mine you just drop it in.
In case you were wondering, the purpose of the triangular hole is to ensure that all fins of the radiator are at least partially exposed to airflow.