Hole
 

What do folks do with the hole under the seat if the original can as been removed to make way for MTC's ..?

Cut a pice of plastic to shape from an old milk carton or whatever and bolt it in place with the two bolts that support the exhaust bracket, then seal round the edges with silicone. Takes ten minutes. If you can be bothered or you're a perfectionist, make one out of aluminium sheet much like the one you get in the box if you buy the official accessory Akrapovic exhaust.

Here's one person's way of doing it...

http://www.xt660.com/showthread.php?t=17143

Thats what i had planned , piece of plastic .