Older mobile home-electrical panel

[jr70895]

Older mobile home and the current outside ac is shot. This mobile home plugs into the power source much like an RV does.
I would like to install a 220 volt 20 amp window unit. I can't afford an electrician but on the other hand don't want any electrical issues.
As you can see lying in front of the panel is the existing cable for the old ac is 6 gauge wire. It was run directly to the ac with no disconnect/breaker box.
Can run new 6 gauge wire to a breaker panel/disconnect attached to the outside of the trailer then run 12 gauge wire to new 220 volt 20 amp plug in?

Is the 6 gauge wire an over-kill for this application? I think the middle outlet is 50 amp and the end outlet is 30 amp. I only need 20 amp for the window unit.

This current central unit was here when the trailer was bought some 15 years ago.