That seems to make the most sense on a single color resto type job.

I'm going to do a van, and will probably do the thing in steps.
Underside
Inside except floor (mask floor)
mask inside and do floor (using tinted bedliner)
Mask off all painted areas and shoot jams and outside (different color).

Since this doesn't have the gaps issues or the removable fenders, it's a bit different.
Final call is the painter preference though, since they are responsible for the final outcome.