Sewing a REALLY bulky item

I may not be understanding you right, but I think what would help would be to whack the seams/folds REALLY well with a mallet. I had a project similar to yours a few years back and it helped IMMENSELY.

Fold over the end, steam it a QUITE a bit, and then either whack it with a small mallet or with a "tailor's clapper." The steam softens the fabric and will help to force the fabric to retain the flatness you've whacked into it. Once you've flattened it, you can stitch around the D ring with no prob. And you won't break any more needles, either. :)

Now, the only problem is for the clapper - they're hard to find. Several years back, you could find them ANYWHERE - nowadays, you have to search the web.

If you go with a mallet, just get a cheap one. You can often find cheapie (but goodies) mallets in the tools section of WallyMart or craft stores often carry them for leatherworking.

HTH!