I was never forced to wear diapers on a road trip when I went on road trips with my parents as a kid however I still wore diapers on a road trip without my parents knowing about it.
I would put disposable baby diapers that would fit me then in my pants legs and pack them in my luggage.
Then I would put a disposable diaper on before the road trip which was Pampers Plastic Backed diapers back then.
The old thick pampers plastic backed diapers held up for an all day road trip so I never needed to change into a new diaper because sometimes I would use the restroom when we stopped to help make the diaper last longer.
Then when we got to the destination I would take my clothes into the bathroom at a relatives house or hotel room and remove the diaper from my pants leg in my other clothes and then change into the new diaper after showering.
I then placed the old diaper into my luggage again in my old clothes and then disposed of them when I got home.
Some parents do force their kids to wear diapers on a road trip and that's okay too and I wished my parents would have made me wear diapers on road trips as I would've loved it.
I wish my parents would've changed my diapers on a road trip as well.
I now wear diapers 24/7 as an adult and wear diapers all the time on road trips and wouldn't be without diapers again.