Wrap the trunks with rope lights and then burlap over that to hold the heat in, if the trees are a manageable height. It won't insure, however, that you won't have leaf burn or even defoliation, but it will ensure that the tree will be able to recover.

Royal-

If you can, Id wait until next spring to plant those Royals if possible. Planting marginal palms this time of year is generally not recommended (although I have been guilty of it several times when I just didnt want to have something sit around in a pot).

As for protection of these palms, the advice on rope lights is good. Try and get the 5.5 W/ft ones though (not the 3 W/ft ones that are many times sold). These lower wattage ones are preferred for all purposes but those used by us when trying to add heat to palms!

Also, be careful about applying too much rope light to the palms, especially on ones which do not have woody clear trunk. I have killed a palm with rope lights (a 10 ft Coconut) and also (temporarily) cosmetically damaged a Bottle and a good sized Royal with them. They put out more heat than one thinks. On parts of the palm that are not woody trunk, its best to have something between the lights and the trunk itself (I typically use fiberglass screening material as this seems to diffuse the heat well and also does not get waterlogged when it rains (as I keep the palms decorated with lights through the holidays, generally from around Thanksgiving to sometime in February, depending on when the last chance for cold is likely to be).

Also---

I would not worry about those zone maps too much as they necessarily are generalized (and making them must be an impossible and thankless job IMO)....just look at whats growing right around you and also any weather stations data for you vicinity. Its also depends on which map is looked at, based on what time period of data was used, as to what "zone" one is in. The last "official" map, done in 1990, is very harsh in its assessments as it contained something like 15 years of data, much of which was from the horrible 1980's! Those years would have certainly tempered one's enthusiasm for growing tender palms in much of Florida.

As mentioned in your other Royal palm thread, there is also a weatherunderground station in your neighborhood that can define your "zone" pretty well.