You need 12v to run the fridge in either AC or gas modes. You can get that 12v with no battery from your converter (makes 12v from 120v) but in the 1985 Rv, not sure how that works.
You could get a battery, but also you need a way to recharge it, so a simple deck mount converter in addition would be a help if the 1985 converter has no charger to it.
In theory you could get a battery and just use any battery charger to recharge it as required, but that could be tiresome, so a converter that stays on would be preferable IMO.
