WOW- I love that William suggested this epic trip!!! (leave it to our bikes to drag us out on such wild adentures).

What about Keen commuter sandals? The footbed is beefy for wide feet and you could put an arch-supporting insole in to give you the support you need (Super Feet, etc). I have wide, flat feet and my Keens are super comfy with my insoles. I absolutely adore my Keens. So much so, in fact, that I wear them when racing triathlons (wore them at my IM last summer). They are breathable, comfortable to walk in, and give you amazingly cool zebra-striped tan lines on your feet!

I had a friend who biked through Yellowstone a few summers ago and said it was bad (rented RV's who have no clue of their girth running him off the road, tons of traffic, etc).

I want to join you. Sounds like an amazing adventure!!!