Any electricians in the house?
This is not a DIY project. Alot of lineman get hurt and electrocuted from power lines getting back-fed by portable generators during outages.
Its a common mistake by homeowners to forget to manually shutoff the panels main breaker, before feeding the panel. Its easy to overlook, especially when the panel is already dead.
The proper way to feed your single panel is with a generator transfer switch.
Joe