I introduced the plastic bag and tarp. He was a little bug- eyed and flinchy, but settled very quickly and stood quietly when I draped the tarp over him.
I was told that he was always ridden in a hackamore because the original owner claimed "he wouldn't take a bit." I tempted him with a drop of molasses on a snaffle, and he opened right up and grabbed the bit into his mouth himself. I plan to keep using the molasses for the next while, then gradually wean him off the sweet stuff.