Regarding bariatric patient handling, apparently one of the big problems with dealing with extremely heavy patients is that it's hard to weigh them (or at least, so I've been told by a doctor friend who works with very very heavy people, >250kg) because they either don't fit on the scale, can't stand on a scale or are too heavy for it. Now, most ambulances (the ones I've seen anyway) have air suspension so you can lower the back and make it easier to roll trolleys in. This is pretty similar to the air suspension on LGVs, just using smaller airbags and a bit less pressure. You could fit a pressure sensor similar to the ones they use on LGVs to the air suspension to tell the difference in weight between the loaded and unloaded ambulance - just calibrate it with the crew on board, just before you get out to load the patient, and then measure again with just the crew and patient on board. It wouldn't be terribly accurate but you could probably measure to within 10kg reasonably easily.