I think there are more and more people travelling with cats, you often don't see them outside, just lounging on the dash of motorhomes. I suspect there are as many in trailers or 5ers.
A six hour trip shouldn't be an issue. When you stop, either take the cat in carrier to the trailer and use the litter box or if there is enough room in the truck, provide the litter box access there during stops.
We didn't take our cat for years and regret that we didn't start earlier as he adjusted so well and really loved the trips we did take.
Doug