cantaloupe
watermelon?

would they still be ok for gliders to eat if frozen?
how long would they be ok in the freezer?

Sure, they'll be fine. They should last several weeks if you're opening the package frequently, or a couple of months if the package remains sealed, or up to a year in a deep freeze - at zero degrees F. The best method is to spread pieces on a cookie sheet and freeze, then package.

Cantaloupe freezes well (as does honeydew and papaya)

I find that watermelon is very mushy when it thaws and my gliders do not eat it as well as the do when it is fresh. I buy watermelon chunks in small amounts (Publix has bowls that are about a pint of cut up fruits) One bowl last 2 or 3 nights for my 10 gliders.