If you want to have 240 volts connected while driving down the road, you most likely will want a waterproof power inlet with a twist lock type locking ring. The one featured below does NOT come with an enclosure box for the interior of the trailer.
You would need to provide your own or mount it such that it is within the present enclosure, if the interior of your trailer is already wired.
Key Features
High quality durable 50A 125V/250V power inlet
316 stainless steel construction for strength and superior corrosion resistance
Nickel plated brass blades provide corrosion resistance to maximize current flow
Cap strap holds cap out of the way to single hand installation of shore power cord
Locking ring compatible with Easy Lock™ sealing rings for a watertight connection
Compatible with conventional shore power cords with threaded lock rings
Open back without rear safety enclosure (not recommended for installation where gear and equipment may accidentally some in contact with connectors
Ideal for recreational and commercial use
Five-year warranty
https://www.westmarine.com/buy/marinco–inlet-50a-125-250v-without-enclosure-stainless-steel–390625?recordNum=27