I may have the same Regency insert, I think there were only 2 models. Home for me is Cherryville in the North Okanagan. No Fortis, only hydro and wood. Part of me says cap it so that no possibility of rain water getting in, the other part of me says leave a vent opening in case you need summer ventilation, although you could run just the fan on the furnace. Maybe PM Richard (Gwizz), he was in the business.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.