I agree with Mountainman. You need to determine the amp draw of all existing appliances on the circuit. In addition, you need to know the amp draw of the items you intend to use the new outlet to power to avoid tripping the breaker.
Just an idea - you could install the new outlet to the frame on curb side, install
a male flanged inlet on the backside, and hardwire the 2 together under the trailer. You then would supply power via an extension card from the parks power to the male flanged inlet on the backside (see picture).