If the VersaMax uses the standard 4-hole Remington thread pattern, my initial thought would be to buy the Aridus CROM RMR mount coming out in the next couple months and then use a Wilson ghost ring front sight. This would give you a good mount for your RMR, plus backup sights.
As for zeroing it... that's going to depend a whole lot on how you're planning to use it. If it were me trying to use buck at standard HD distances... maybe 15yds. If I thought I was going to have to toss slugs further, well, maybe more like 25-50yds. The good thing about shotguns is that you've got low height over bore, so you won't need to have a substantial holdover at closer ranges like you would on an AR.