Looks like it's going to get a bit cold for my tender not-yet-sprouting sproutlings, so I've built a little cold frame out of PVC and a clear plastic painter's tarp this afternoon. It took about two hours to make, partly because I was being really careful to make sure it fit correctly, but I'm pretty pleased with it. I don't think the painter's tarp will last that long, but I've got another one (same package; bought one, cut it in half for the exact size I needed - lucky!) and eventually I'll probably make that part out of something better.
Anyway, if you have anything particularly tender out, it might be good to protect it a bit later this week and this week-end, particularly if you're away from the water.