The trunk is the same size since it's the same body panel with the tire well and cover like all GP's. I just have the fix-a-flat and compressor. I guess there is more room since I put some tools and more fix-a-flat in the spare tire well in case I get two flats.
The owner's manual says sidewall blowouts are very rare. Anyway I guess with pontiac roadside and onstar, I could call both to see who gets there first.