It was a couple of years ago now but I used to do a six hour trip across the uk and back once a week. This caused a few issues like eating while on the move that seemed to upset my stomach. One time about 8am in the morning stuck in rush hour traffic around a large town I literally had to pull up the 4x4 and trailer onto the embankment and run out to drop a load behind the nearest bush. A horrific thing for a gal to have to do at the best of times let alone when its a runny mess!
After that I decided that wearing a nappy just in-case would be a good idea, also being a DL it added a good bit of fun to the drive. They only really saved me inconvenience or emergency stops a couple of times, I did have difficulty letting go to wee for a bit which is not normally a problem. After a while of relaxing and concentrating on driving, my bladder just decided that in a car was no different than any where else when nappied and just started leak as it does normally when I am nappied. After my nappies had dealt with a stomach upset while driving it was no longer a issue at all. After all if you have a full mess squidging back and fourth in your nappy what does a little water hurt?
For anyone with any interest I did eventually discern what was causing my tummy upsets while driving, it was not just the vibrations of driving along as I thought, I was partaking of sugar free mints and chewing gum while driving, to many sugar free mints make a explosive combination!