Thanks, Sher! Jimmy's new "belts" arrived yesterday, and judging by the indignant look on his face, they are not as comfortable as the towel I taped around his middle the previous night. However, washing a king-sized mattress pad almost killed my elderly washing machine, so wearing this to bed at night (or if we leave for several hours) is mandatory now. I added a pantyliner, which seemed to catch the bit of dribble overnight.
I WILL take him to the Vet here in FL - if there's medication that could help, I'd happily give it a try as long as it's safe for diabetic dogs. Otherwise, we're taking him outdoors about every other hour to empty his bladder, and that seems to be helping?