If you use just one propane tank with your trailer or motorhome, you need a regulator with two stages, but designed for one tank.
This premium Cavagna two-stage regulator is exactly what you need for safe and reliable gas supply on your one-tank system. This version is designed for mounting horizontally so that the vent always points down when mounted. Pointing the vent down keeps it clean and functioning properly.
Whether your propane tank is vertical or horizontal does not determine how you mount the regulator.