These make the most sense for our application.

http://www.coastfab.com/mufflers.html

One can inspect the guts of the  muffler from time to time to
make sure it is not plugging up. Can be over hauled if necessary.
A perforated Inconel tube could be added internally to handle our
1700 F.

They are also the lowest drag configuration.

They could be as much as four feet long without adding
much to the drag if you have an airport noise problem.

Finally a viable rotary muffler solution.

These people have a great printed catalog for our purposes.
Much better than the web site.

Tons of useful bits and pieces.

Paul Lamar