If you are going to Bar Fifty, be aware that the roads approaching Bismark and on to the ride, are curvy 2 lane roads, not 55 mph roads....the horses should be A-ok on the water deal, they probably won't drink any on that short of a haul, and maybe not til that eve anyway.  I would offer but not be surprised if they don't drink any enroute.

I am so doing a LD haul- I make stops primarily for me,food,pop and bathroom breaks. I have hung a water bucket before but I doubt he drank any,it mostly appeared to just splash out. The horses are fine in the trailer ( there was a recent study done suggesting horses are just fine without repeated stops) I have felt it was better to get there rather than prolong it by stopping to rest.

I don't drive 55 on the interstate. I try to keep it about 70ish....

Some horses won't eat hay while hauling and some do. most horses can survivie several hours without eating anyway so hay bags is a personal perference.

I would not hang a bucket in the trailer!

It sounds like a wreck waiting to happen, I can just see one of mine getting the rings on the halter through the bale on the bucket!!!! I would offer water (  if you have drops on the heads) when I stopped for gas.  I always do this but my horses think it is much more fun to spit water on my head than drink it!! But still I try!  Really, they should be fine for four hours with out water as long as you water them as soon as you get there.