Are you talking about an "older water heater with a pilot light that gets blown our" or are you talking about a "more recent water heater and the actual full flame gets blown out" ???
It's essential that the year and model water heater is known and just "which flame" is being blown out.
As Danny suggested, if you can't reposition the trailer so the prevailing wind gusts are not hitting the water heater, then possibly a couple of steel fence posts" (think about them as heavy duty tent poles" and then a piece of an old plastic patio mat or an old sun shade sail or something else that wind can "blow through" but reduce the velocity of the wind" wired between them as a wind block. Mount it about 4 or 5 feet out from the trailer, so it will block the gusts, but not be close enough to the trailer to get hot or if the wind blows it over, it won't hit the trailer.
2015 F250 6.7l 4x4
2014 Cougar X Lite 27RKS