I just installed a 12v outlet in my trailer. I bought it from Crappy Tire:
Auxiliary Power Source Outlet
I also bought and installed an inline fuse before the 12v socket. This was handy as if you wire the 12v outlet backwards (which I did, see note below) it pops the inline fuse and doesn't hit your convertor.
ATM Inline Fuse
Note that the wiring on your scamp
is 'proabably' black positive and white negative whereas the Crappy Tire 12v outlet is red positive and black negative. I was just learning 12v when I first did this and I now use my multi-meter to tell me what's really happening.