I haven't used anything yet.
I'll probably end up getting some 4" slash cut tips and then use the 5" Chrome strap from O'Reilly's to mount them on the existing pipe with.
Then I'll more than likely use a chunk of re-rod welded to the frame at the rear to steady it.
It will basically be the same way I mounted the home made tips on the Chevy Trike.

Right below the firewall, you will see a yellowish strip on the header and muffler. That is the strip I'm talking about. Then on the rear of the muffler is a piece of re-rod bent to fit the rear of the curved extension and welded to the frame above it. Quick and dirty muffler bracket.