It just depends on what you are able to do electrical
wise or are willing to pay for. Easy as buying a smart battery charger and plugging in the battery charger when you need it or wiring in a charger all the way to replacing the main 120 circuit and wiring in a new load center with built in converter and smart battery charger.
Do a search on this site and the internet for the PD4045 a more modern charging/load center for small to midsize RV. I went this way with my trailer because I wanted to add more circuits both 120 volt AC and 12 volt DC. I went over kill and separated all of my runs so there was almost no daisy chaining of loads. I also added solar
capability so big changes in the electrical
system on my trailer.
Once you get your trailer and take it camping you will know more of what you want. Camping alone in the boondocks is far different than people that don't venture any further than a KOA with full hook-ups.
There is a lot to be said to keeping it simple.
With almost 40 years between when your trailer was built to the electrical
demands of the younger generations of today's youth and what you deem comfortable to meet your needs the power grid can be significantly different.
Camping with a family group we had cell phones, tablets, camera battery's and my own personal dvd player sucking battery juice from our trailer all the time in a campground with no power. 2 small solar
panels keeping it all up by day. No generator
or car running to charge the battery or provide 120 volt AC. Times have changed since 1977 when your trailer was built.