I decided to try one more time before I gave up. I didn't have the heart to make muffins that one of them couldn't have.
Here's what I did based on my favorite recipe that always works...
Whisk (or sift) together in small bowl:
2c brown rice flour
1/4c tapioca starch
1/4c potato starch
2t guar gum
1t baking soda
1 1/2 c raw sugar
1/2 c shortening
6T ground flax (or 3 beaten eggs)
2c mashed banana (could substitute 15 oz pumpkin and spices on can, or applesauce and cinnamon)
Add dry to wet and stir just until moistened. Bake at 350 for 60-65 minutes for loaves, 25-30 minutes for muffins.