Lets take a gander at the Warbonnet Undercover/Poncho make just for the RidgeRunner hammock.
Since the tarp pitch on a Bridge Hammock requires a wider spread and in some cases a slightly higher pitch....an undercover is a good way to ensure extra protection from wind and blown rain. Also holds in some heat.
From the Warbonnet website:
"The undercover is just that, a waterproof cover that protects the bottom of the Ridgerunner from moisture. It's made of tarp fabric and protects the bottom of the hammock (or your underquilt) from windblown moisture that might come in under the sides/ends of your tarp in severe conditions. It is also available with an attached hood so it doubles as a poncho."