To me it ovious that every tank is designed with a top and bottom and proper way to haul it down the road.
7 20 30 lbs tanks seen in RV's are basically the same vertical design.
Forklifts are designed to be used horizontal with a pin locating them in a specific location on the lift, but its easy to have them vertical in storage and shipping, and in their designed scenario horizontal with the important bits at the top.
permanently mounted tanks are the same,, this isn't supposed to be complicated.
Years ago I worked for a rental place I picked up 15 empty 100Lb tanks, brought them back and filled every last one of them the next morning so we could bill out the customer, come mid day every last tank was venting off I bet I filled them at 40 degrees outside and mid day was about 75... Needless to say everyone stayed away from these tanks. until the plum was gone.
So in a car right after you filled them... not the best idea in my book.
Please note I suspect the 80% float valves you see in the 20lb and 30lb tanks I suspect were implemented simply to keep people safe as people would put them in cars.