the way I understand it, and this is a VERY complicated subject that I've yet to be able to get any sort of clear answer.
You are OK with no restrictions IF the following are met
You are not transporting in commerce
You are transporting less than 1000lbs of cylinders *total cylinder weight, valve/bottle/gas*
The less than 1000lbs is pretty clear, sort of, but I would recommend abiding by it. Generally speaking that is about 25 AL80's. The odds of any state trooper having any clue what this means or even thinking about looking at it is near 0 and if you call your states highway patrol, good luck finding anyone who can give you an answer. I've called NC/SC/GA/FL's highway patrols and not a single one has been able to give me an answer about the weight or definition of commerce.
The commerce gets a little weird.
The way I understand it is the following weird situation applies that can bite people. You transport rental tanks for students/friends if they are not in the vehicle with you. If they're in the vehicle with you, happy days, if YOU rented the tank and let them use it, happy days, but if you picked it up for them, then you are technically transporting that bottle in commerce and then have to do a bunch of really annoying stuff.
TLDR, you'll probably be ok driving around like normal which is what we all do, just don't do anything stupid and certainly don't open your mouth if you get pulled over.