I've read a lot of posts about the saito flex mufflers cracking in two. I'm about to mount one on my 1.20 what are some mounting techniques to avoid this problem? Will have it traveling through a piece in 1/2" think plywood on its way out of the plane is this enough support? All feed back greatly appreciated.

The flex pipe needs to be supported at the end. Either by putting a bracket on the muffler( If used) or by holding the end of the flex pipe. The reason some people have had cracks is they leave it unsupported, and vibration causes it to crack
Rick

You will also want to put some cushion aroung the end to take more vibration off of the muffler. I used adhesive backed foam and put a couple layers on.

I used an electrical P-clip that had rubber inside it. Clamped it around it and it holds it but can still move a tad bit due to the rubber.

the heat didn't melt the foam? Also my muffler didn't come with a pressure tap. Could I tap the end and install a nipple would that work?

Yes, you can tap into the muffler and add a pressure nipple.