I like the idea of touring on an MTB, but the one I have and use for commuting is short. I have to use small panniers to avoid heelstrike. If I go on a tour, I'd like to be able to put larger panniers. Are there any long wheelbase MTB frames known to be good for this purpose or touring frames that use 26" MTB wheels and have disc mounts? I also imagine a longer frame would be more comfortable, no?

Edit: to clarify, I'm looking for a frame only, not a complete bike.

Adam