MH's sit more then they move and those calipers love to stick. I could never figure out what it was that made them do that. What I did figure out was if I put the rig in reverse and back up 50-100 feet while pumping the brakes I could usually free them up.
Even when the rig is moving daily they can stick. I was driving from the north to south and was in Florida near Destin when two bikers cut in front of me and hit the brakes to make a right turn. I slammed on the brakes and thought I was going to kill them. Luckily those brakes held. About 4 miles down the road both front calipers stuck shut.
Limped into the park for the night. They did free up just enough in the morning to make it to a truck stop for repairs. For me the brakes were a constant battle, and I had to always be on top of them to avoid problems.
BTW, I had all new top line loaded calipers by the time I was done and still had issues from time to time. Taking the temps will tell you when one is starting to stick before it becomes a bigger issue. Changing the fluid every couple of years will help with that soft pedal feel. Ford even came out with a special brake fluid for that F53 which had a higher boiling point trying to fix the problem.