The link that Dennis gave you will be a start. As others have posted, your 150+ foot run is going to lose a lot. Have your license electrician give you his gauge needed, not you telling him. Remember its your RV that is going to get smoked. If you wire it for just the refrigerator and someone turns on the AC then kiss the AC motors good by if it does not blow the breaker. They will over heat. As others stated, wire it for the plug on the RV , then if you are not around and someone else turns on something, then all is well.
http://www.cerrowire.com/voltage-drop-table