I would use leaves as they are more flammable.

Would? or wouldn'tuse leaves, Jim?

Flammable is why I never used leaves inside an enclosure.
Each year, the odd dry maple leaf blows inside palm enclosures while I'm installing the covers.

With C-9 incandescents lying on the ground heating the enclosures all winter, I'm always amazed at just how brittle those few dry leaves have become over winter.
They basically turn to dust when I open up enclosures in late winter.

Too risky.

Duke, I like the idea of those forms...I think they're called Sonatubes here.
They wouldn't get wet if you enclose the entire structure (after installing a garbage can lid on top) if you overwrap with plastic, say, a 6 ml vapor barrier.

Barb

I covered a large sabal minor two years ago for the first freeze event of the year, using a sonotube, rope and a vapor barrier tent. It was well secured, yet blew over. The sonotube got soft. I wouldn't use one again. The humidity causes them to fail.

Good point, Adam.

We're still relatively warm, so I haven't yet needed to protect the palms yet. I'm reconsidering the tubes, due to the comments. At least for this year, I can store the palms in the garage with less trouble then building a box. Thanks for the replies.