If I were you, I'd make 2 reservations. One for the van and one for midsize. You may get lucky and get a van i the emerald/exec section. If not, you dont want to be paying fees to upgrade to a van etc or risk chancing it on them giving you a van even though you are an exec member.

Then cancel the other res when you get there.

GL

I didn't see a van the last 2 times I went there but did see one the 2 times before... Most likely they would get you into a van but you never know.