Puckdropper said:

No frost yet, but watermelon that are just now starting to produce quite
a bit of fruit. (I haven't looked in a few days, haven't been around.)

Is there a easy and fairly inexpensive way to help keep the plants warm
enough at night?

Old sheets, blankets, towels, newspapers, and paper grocery bags are what
get pressed into service at my house. When I 'retire' sheets and towels
they get stockpiled for all sorts of projects and emergencies.

They do yard waste pickup here in large paper bags, which we accumulate
each fall when we scarf leaves from around the neighborhood. The big
bags are great for covering plants when frost threatens.
--
Pat in Plymouth MI ('someplace.net' is comcast)

Any technology distinguishable from magic is insufficiently advanced.
(attributed to Don Marti)