Following surgery in '01, I was diaper-dependent for several years and
learned to pee virtually everywhere in every circumstance of necessity.
For a non-stop drive from the Tampa Area of Florida to my home in
Muskoka, Ontario, I once wore a thick cotton diaper with thick cotton
insert and, inside those, used a toddler-sized disposable (with holes
cut through the plastic liner). No change was required enroute, though I
limited my intake of liquids to less coffee than I'd preferred!
Needless to say, the diaper(s) were thoroughly saturated at my destination
and a mere drop away from torrential leaking.
Yes, it does help to use your legs (or an arm) to take a bit of weight off the seat.