I have to retract my recommendation of sandals based on further consideration of Ryan’s determination to walk 40+ miles/day. I have never walked that much for more than 1 day in sucession, neither in sandals nor in any type of shoes, neither with nor without a backpack. I have no desire to push my limits.
The reason sandals work for me is that I walk on the front of my foot, which makes the muscles of the foot work extremely hard, which in turn keeps them warm in fairly cold temperatures. These strong muscles also protect me from injury, which is why the lack of any support in the sandals in no problem for me, even in the mountains, even on scree slopes. (I most certainly do not “ski” down scree slopes, or if I do, I go very slowly so as not to break a leg, and sandals work fine when going slowly.) However, I need considerably rest time each night to allow any tissue injuries to those hard-working foot muscles to be repaired. I don’t see this as a problem, since I get bored after hiking more than 6 hours and so there is always plenty of rest time available. But for someone who is determined to walk 40+ miles/day, there won’t be much rest time, and thus it is essential to avoid any sort of tissue damage. And so yes, all this hocus-pocus with orthotics and whatnot is probably necessary.
Personally, I think a far smarter approach would be to take the advice someone gave about catching fish to supplement the food supply. This would reduce the need to walk so many miles/day. Also, as we discussed ad nauseum in the food discussion, the only way to access the body’s fat reserves is to go slow. With 40+ miles/day, the body will probably be burning lots of glucose and all this will have to be carried. Regardless of this issue, I think 40+ miles/day, carrying a heavy pack, off-trail, for weeks in succession, may lead to some sort of injury, no matter what sort of orthotics or footwear is used. Then again, some people can indeed walk high mileage day after day without stress injuries.

