I'm going to guess the damage is low on the shrub and not located where you could follow conventional advice and remove anything torn or jagged :)

I don't think 1x5 should cause irreparable harm in a rhododendron that large, especially if it has time to heal before a major freezing storm comes your way. Probably the best thing to do is nothing at all and let the rhody take care of itself. I wouldn't use a sealer or paint - You want the wood to dry - then the cambium layer forms what's called "wound wood" around the wound and closes it. Pruning paint may deter/inhibit that process.

morz8, thanks very much for your advice. This is on the main trunk of the shrub so it would be impossible for me to prune. I will keep an eye on it and hope it will heal before the cold weather. Thanks again.