Protecting Seedlings From A Late Freeze

This is a very theoretical even exotic question for me, given where I live and maybe that is why I found it interesting.

How do you protect seedlings from a late freeze?

The solution  - building a Styrofoam box to cover them - isn’t very complicated or expensive, but is kind of time consuming, and if this was something I had to deal with, I would probably build a good and strong one so that I could reuse it again and again over the years.

One thing I can add to what Backyard Gardening said about building this box, is how to weigh it down so it wouldn’t fly away - If you glue or pin in tabs with holes or loops of wire properly secured, you can use stakes  (like u shaped tent stakes) to tether the box down to the ground, instead of weighing it down by piling a bunch of stuff on it.

Photo credit, creative commons license Floben