Since I did figure out a passable design for the BatToa Droid, I couldn't resist seeing if I could tweak it into a usable design for the other three basic variants. This is my least favorite, since there's nothing for the hands to hold, so the arms basically hang there useless, and posing them with bent elbows so they don't look weird is a bit tricky. I'm still not thrilled with the pose, but the only alternative was to replace the arms with bulkier POHATU legs, and that wouldn't look right on a BatToa Droid.
I thought the basic BatToa Droid looked goofy, and then I had to figure out how to remove the backpack. The result is a wafer-thin torso and a big hump on the back. I much prefer having the backpack to help fill out the torso a bit, though I have to admit that the odd look of the torso complements the look of pretty much everything else.