Nice writeup! I really appreciate you sharing your results, even if they weren't as good as hoped. I have a very similar side-venting setup and improved the dead space issue using regular fiberglass insulation. It does keep the counter top above the fridge MUCH cooler, so that's got to help some (
pic here). I also hard-wired a fan inside the fridge (
pic here). I think the most helpful part there is air flow when I overcrowd the fridge -- easy to do when it's small. Please keep us updated with your endeavors! I too worry when temps get above 90°. Just doesn't seem to keep up no matter what.