I completely ran out of Titanium White (funny how that happens) so I ran to the rip-off art store nearby. While there I saw some masonite boards prepped with gesso, so I thought I'd try one out. Several of you have suggested I try this slicker surface since it's one of the qualities I enjoy in doing the postcards.
I have to say it really appealed to me. I did a dark wash first to tone down the stark white of the gesso. The I just went to town like I do with the postcards. Since it's a larger surface (9x12 inches) I did wind up putting in more detail than on the 4x6 postcard, but without getting overly fussy.