I found that for me, using two straps is the most comfortable setup. I bought a set of regular accordion strap brackets from a local dealer and mounted them on the top and bottom , similar to a larger 2 or 3 row accordion. I find that this setup stabilizes the accordion. I rest my thumb on the edge of the keyboard just like I would with an Irish accordion. I don't use the thumb strap at all, instead I am able to move my hand up and down. This keeps my wrists straight and relieves a lot of stress on the left shoulder. It also eliminates the pain in my wrists that comes from bending them when playing. This is important for those with arthritis, and tendonitis. I know this is unorthodox for Cajun accordion, but it works very nicely for me. Give it some thought.
Thanks to everybody for your replies. Would it be possible to post a photo of you personal strap bracket set-up? A thousand words, and all that. As I've said, I wish to hold off on the wood butchery until I'm sure of the results.
Okay, I didn't want to say it first, but, DANGER JIM ROBERTSON! Your box is gonna get messed up. Eventually if not before eventually. If you sit with an accordion, you will lay with an accordion (my Paw Paw always said), and if you stand with a band you will land many fans (my Maw Maw always said). So if you strap, learn to rap. I've always like the D-Rings, me. I use them swivel lobster claw type latch hooks that you can get for cheap at Home Deposit. They really work out well and will eliminate the permanently buckled strap solution that plagues many boxes inside the thinker. Expect scars and scratches. That means progress. Look at Willie Nelson.
Just fitted D-rings to a Tim Reed; pre-drill the holes correctly with the exact drill bits not wider than the screw's core and thus well inside the threading to avoid leaking. Remove the drilling wood dust from the accordions interior too, otherwise it will endup blocking reeds. I used wide headed plate screws with double washers the same with to disperse stress and avoid scratching the accordion and corner pieces by the D-ring's base plate. You can use Larry Miller's way as Nick suggested, but that involves more drilling and hole making, and the D-ring's base plate is made of tough material. Don't drill that part when fitted to the accordion in case your drill skips sideways. PS i have locally and specially made straps with delrin hooks for sale occasionally ....
(photos temporarily posted, please download if you need them)