Your 54 will have very limited 12V
wiring, most of the electrical would have been 110V in 54.
Since you are restoring your trailer, I suggest rewiring with as many12V circuits as is practical to you. Then, add a good quality battery and converter/charger such as the Intellipower 45A or 60A, and you're good to go.
check out my thread "a63 for me", I rewired my 1963
Overlander completely. It has all fans and light running on 12V
now, so that it's function will be the same, boondocking or plugged in. I won't have A/C witout being plugged into a 30A outlet, plus my 12V
outlets will not work, but everything else will function the same.
If you search the forums, using the search function, you will find more info on this than you ca digest in a month....
Good Luck with your project. A 54 Flying Cloud is definitely a worth while trailer to restore.