You could try some pipe lagging on the hose to provide some extra insulation and wouldn't cost too much.
I have found that the water in the hose when not running rarely freezes unless it gets well below freezing. If you suspect the water in the hose has frozen at any time, disconnect the hose from the RO and pour some warm water on the hose, then flush the hose through until ice is cleared and water runs freely.
Then connect back up to the RO.