Hi Dee Dee,
I was surprised by the number of folks that I saw out there who were doing exactly as you described going to get shots so that they could paint them later.  THere were at least two folks I met in the Gros Ventre Campgrounds who were doing this.
This trip was an interesting one for several reasons.  We spent very little time in Yellowstone this trip.  I only ventured up there twice.  THere was just so much to shoot in the Tetons.  The moose were amazing...and the foliage was out of this world.
James