Bare in mind we are talking cylinders here.
Tank is something permanently attached to RV.
My 1972 bus conversion had propane tank in it. Funny, back in 1970's the RV propane tanks did not exist, so converter used 40 gallons residential tank and fit it in bus basement. That thing never needed and still doesn't need recertification as it falls under different laws than portable cylinders.
The only issues I had refilling it was making declaration that propane is not used as motor fuel.
I do like horizontal cylinders, not only for their gauges, but also for easy operation.
Had 2 vertical, 7 gallons cylinders in Lance and refilling the inner one was quite a task. Especially when loaded high on the truck.
Then I never knew how much propane I had.