Mark. Gooley wrote:

Here I am in zone 8b, but with most of my roses lacking
canopy cover (it gets in the way of the Florida sun), a
light frost can be somewhat intensified by heat radiating
off into (ultimately) outer space on cold, clear nights.

NOT an issue. You do not need to protect your established roses
from cold in your zone, and probably not your babies, either.

Like you, we have some cold snaps cold enough to damage--in
five years I lost a single baby ownroort--however, also
like you, any significant organic winter protection (like
mulch) will increase the incidence of rot and fungus.



(18 to 20F is about as cold as it gets here in a typical winter,
with temperatures typically well above freezing before the
following noon, and if I can keep these little plants (still mostly
in pots) from losing their new growth, I might be glad of it later.
The 8 degrees F or so of protection the cloth can provide might
suffice to do just that.)


If you want to cover them, do it--but a better idea would be
to simply move them close to your house.