The obvious outside differences I'll ignore.
If you look inside on a panel above the 'tubs' the walls are open to the outer panel with some vertical structure stuff. On a Suburban that area is finished all the way up to the headliner.
From what I can tell the biggest difference from a rust standpoint is the passenger compartment windows. Both my Suburbans are rusty around teh windows, and the panels underneath are rusty from apparent window leaks.
Come over and look at mine sometime.
Also take a look at RB's Urban Suburban from a couple years ago. They started this project with a panel if I remember correctly.
http://www.classictrucks.com/features/0405cl_1947_chevy_panel_truck/photo_01.html
