Yes, when frost kills the foliage, they can be saved the same way. You can also save Colocasia (elephant ear,) and Gladiolus if you think the short-lived flowers are worth it. Are you having a great show of Canna blooms?

I planted mine in my shade garden - "free-form". They are a delight. I am planning on covering the area in black plastic for the winter (Upstate South Carolina). The garden gets plenty of sun when the leaves fall so I am hoping it stays toasty under there. I don't want to dig them up.

Here's hoping...

Stunning, LK! Too much moisture while cold is usually what creates the hardiness 'barrier' for a lot of plants, so the idea of keeping them more dry is good, and it's already raised, that bed, also good, beats any possible drainage issues in the surrounding soil.

The heat, I'm not so sure about, what if it's so warm they want to grow too soon? IDK if that's a concern or not. Hopefully someone more qualified might jump in here. A couple feet of leaves might be a good alternative. That's my usual method for zone-cheating, (combined with a 'high spot' like you have,) works well. Just don't panic in the spring. I didn't see Cals sprout here until May this year. They weren't at all fooled by the heat in March, like they knew a fluke frost was coming.

I have saved them, in only slightly damp peat moss, in a plastic bag at a temp about 50 degrees, but cannot get them started without evenly moist soil and a temp of 80 degrees. That, to me, means a greenhouse, that I once had available. Not now, so I buy plants in the warm Spring, instead.

you should not wait until the frost to dig out caladiums. the frost can damage the corms. besides when it's wet and cool - the corms might rot very easily or mildew.
the leaves will start declining anyway when temps go below 65F. they need soil at min 75F (higher is better) to sprout. if you put them in shallow plastic grocery tubs with lids on south window and dampen the peat slightly, keeping them somewhat covered with the lid and slightly damp - they will sprout in about a month. but if the night temps drop below 65F - it will take much longer. bottom heat from radiator/heading pad helps a lot to speed things up.
when caladium tubers are very small (less then half inch) - it's better to keep them in a pot overwinter , dry.
when the leaves have declined (lost color completely and wilted) but still attached, trim the stalk to 2-3 " and then dig them up soon after - you'll know exactly where the tubers are when stems are still showing. let them dry up for a few days in shade or in the garage - free of rain. then you can gently brush them with a brush from soil (toothbrush serves well) and pull the dry stems off and dried up roots. then you can put them in shallow pots with peat/starter soil and keep them cool - 50F ok, but 60F is fine too. do not put them in the fridge. check them in march for growing tips. you can start sprouting them in mar or in april or even in may.
depending on how large the shoots are.