As far as a electrical outlet without a box in the wall goes..
Is it possible? sure, but highly doubtful.
Thin walls of a RV make wiring standard outlets with a box a challenge but not impossible.
They make these..
Click For Full-Size Image.
Which are low profile shallow work box with a "side car", the box is mounted on the other side of the wall and the outlet helps to hold the box in place. They are hidden and unless you know what you are working with are easily mistaken for having no workbox behind it.
The side car provides the means for the wire to enter/exit and enough fill room to accommodate more than one Romex entry/exit. Older boxes like the grey one do not have any clamps, the newer in blue does have plastic clamps that when you push the Romex through prevents the Romex from pulling back out.
My first TT used the all in one vampire tap "speed wire" outlets, my current TT used the low profile shallow work boxes with side car..
I will take the low profile workbox with side car and real outlets any time of the day.. It shows the manufacturer actually took quality to a higher level.