Agree with the others, but chances are that few of the potentially damaged items are actually defunct. Fridge boards and the converter/charger itself seem to be the most susceptible, but there are no guarantees. You will just have to try them to see.
With any sort of luck, the converter had reverse polarity fuses that blew out when the battery was hooked up backwards, but those weren't real common back in 1998. If you can identify the make/model of the converter or power center (combo 120v breakers & 12v fuses), we can probably tell if it has that protection or not.
Hooking the battery up backwards to get the lights to work makes me think there may have been a major short to ground on the 12v plus side, either near the battery plus cable or on one of the main branch power feeds from the 12v distribution panel to lights and such. It may still be there and need fixing. Obviously the former owner was no electrician.