Freezing seeds

Is storing seeds in the freezer a good idea in general?

Specifically for cantaloupe and cucumbers?

Once frozen, do they have to stay in the freezer? I read one reference about freezing them just for a while to kill insects.

Freezing seeds is usually a good idea if you want to keep them longer than their typical period of viability.  Freezing can keep seeds viable for decades.  Orthodox seeds can be frozen indefinitely as long as they are fully dried.  It is best not to warm them up and refreeze because of the risk of condensation and possible metabolic effects but, in practice, you will usually get away with it.  I package seeds for long term storage in quantities that I would be likely to use so that I don't have to remove them all and put some back.

Recalcitrant seeds cannot be frozen, but these are usually seeds of tropical plants that aren't commonly grown from seed.

Storing dry seeds, of common vegetables, in the freezer basically gives them an incredibly long storage life.  I would store all my seeds in the freezer if I had space for them there. It's more important for me to store food in the freezer.

I take bulk seeds out of the freezer, thaw them to take out this year's sample, then return them to the freezer.

I try to cycle all varieties of seed through the freezer to kill seed born insects. That is particularly important for seeds that people send me in the mail. I really don't want to be importing any more seed eating insect species to my farm.

Freezing seeds often mimics their nature life cycle so it is good to freeze native seeds like wildflowers.

One note of caution...

Make certain your seeds are entirely dry. Seeds like tomato, etc. will snap in half when properly dry. Bean seeds will shatter when hit with a hammer. If you put seeds in the freezer that are not dry, the seeds will develop ice crystals in them that will kill the seeds. Before I found this information, I stored some beans seeds in the freezer that appeared to be dry, and I killed them.