LPG (or "Camping-gas") for camping is a mess here in Europe. Lots of different bottles and connectors that vary by country. You are not legally allowed to fill your own bottles, either. The euro bottle sizes do not fit inside the gas compartment of a US RV. To top it all off, there is the general sentiment that the local system is much better and safer...
Technically, LPG is available at many gas stations, because many cars are using it. But not in all european countries, so you need read up on that beforehand. Provided you brought the correct set of adapters, you _can_ fill your US bottles at these pumps, no problem. And cheaply, too. You may run into the odd attendant who informs you that what you are doing is ver-bo-ten. Some of them may take pity and fill the bottle for you. Some may chase you away.
LPG is always a mixture of propane and butane here. The pre-filled bottles in the more southern regions can come with pure butane. They will still work fine as long as temps don't fall below freezing (butane does not evaporate below around 30F).
Another thing you probable need to be aware of is the size and weight of your rig.
It is too high for a number of underpasses in the back country and in old villages. You need to be alert and keep an eye on the signage.
And you weigh more than 3.5 metric tonnes. That is a magic legal border in Europe above which a number of regulations change. In daily life you will note that a number of small roads and brigdes are blocked by signs that say "3,5 t". And the way road tolls are calculated (another mess, as every country has its own way of doing it) changes. Obviously, tolls for your big truck are more expensive, too.
