Hi man!
Good to know trucks stops exist here and gusjuging is also done in Canada. I thought it was an U.S. thing.
Past April I traveled many different southern states, mostly caravaning with people I met at a Rainbow gathering in Texas, from TX to another gathering in Arizona. We were about 18 dirty hippies and a three dogs, in two cars and a van, and none on of us spent money on guys, neither many other travelers from the gatherings. Gusjugging is very common down there, you might even run into more people doing the same in little gas stations (it happened to me getting to California).
Anyway, useful info: As you know, the best places are the truck stops, and the best people, truckers. Now there are a few big truck stops companies in the states: Love's, Pilot and Flying J's. Sometimes, after a while without being lucky, we got kicked out of certain spots, since all Love's and Pilot have "No Soliciting" signs and eventually somebody might get pissed off and warn the gas station workers. But everyone says Flying J's are the most friendly towards hitchhikers and gas juggers, so keep that in mind.
The one you'll see the most is Love's, they are aaaall over the country, specially the southern states. Often you'll find there are several truck stops at the same junction, so if you get kicked out of once just switch to the other one.
Another funny thing, police are obliged to help you out with twenty bucks of gas if you ask for their help on their station in each town. They'll make you identify yourself though, and sign a little document, but then they lead you to their private gas place and fill part of your tank. We (the crew in my car) did it once in New Mexico and someone said you can only do this once in each state, but one of the drivers of the caravan claimed to have done it twice, so I am not sure about it. I doubt you can go town by town doing this, eventually they would realize, but even if you can it might be quicker to just gasjug. But this can help you keep going on a desperate quite night in the middle of nowhere.
Be careful when heading from west AZ into Cali, there is a looong fucking way in which there is nothing but desert along the interstate (like 100 or 150 miles) so you want to make sure you fill up your tank before getting into that.
As for laws, I don't think this has even been legislated beyond the usual laws about soliciting and all that. We personally never had any trouble with police regarding gasjuging, but just in case don't do it if their at the spot, they don't like anything that escapes their understanding and lifestyles (hippies, punks, travelers, etc...) and might give you shit just for sake of it. There is a lot of police in the south, and you will most probably be stopped and searched at some point if you are look "different" in any way (we did), so try to be subtle. Speed limits are very enforced some times, so respect the ones getting in and out of town areas. And be careful about weed, specially in Texas, they have very stupid strict laws, and you can be arrested or fined just for having parafernalia (a grinder or rolling paper is enough) even if you don't carry any drug with you at all.
Save travels my friend. Peace.
Carlos Dreem