I'm sure that there must be many ways to skin this cat but here is how I did it.

Glued door seal to door with silicone before prime.  Also added a thin rubber mating strip to door opening surround, again before prime.

When ready to paint, removed door and masked door seal ( and door interior), then painted door.   When ready to paint body, masked  mating strip and  entire door opening,  then painted door opening surround. I am using "Ranthane" to paint my L-IVP.  Paint is a 2-part polyurathane and it is heavy.  Anything that is covered by upholstry I decided not to paint, just to reduce the weight a little.  Hope this helps.

Regards, Bill Hogarty