Crewcab build

[Frizzle Fry]

Alright hopefully your roof will end-up looking better than this but here's the mspaint version of one possible approach...

Cut the front/lower edge off the rear doors and make an entire new front edge of the rear doors using the rear cab portion of the front door jam. In other words weld the striker section from the cab that would have been your B-Pilar to the front of the rear doors. Yes, this will make it so you have to open the front doors in order to open the rear doors, but I think that's the price of going pillarless. It will also simplify the weather-strip situation.

In this pic I also angled the rear window frame forward a bit to match the angle of the front door window frame reducing the "V" shape between the windows. If you do this you'll have to have custom wing windows cut. ...or just live with the "V" ...or tilt the front window frame back to match the rear... options