One thing to keep in mind, since you are considering the aluminum or composite tanks in order to reduce tongue weight, is that they are not all that much lighter than steel tanks when they are full (or nearly full). That's because the
propane still weighs the same amount no matter what type of tank you have it in.
Now, I'm not saying they're not lighter, or that they are a bad purchase, but just know that once you have a full tank, the percentage that they are lighter goes way down.
Here is some data for 20# tanks:
Type.................empty (tare) weight...............full weight
Steel......................16.6 lbs..............................~36 lbs
Aluminum...............14.2 lbs..............................~34 lbs
Composite..............12.8 lbs..............................~32.5 lbs
Steel and aluminum data from Worthington Cylinder and composite data from Lite Cylinder.
So to my mind, the greatest benefit to steel's alternatives are as follows:
Aluminum: Doesn't rust and slightly lighter when empty (but not very much)
Composite: Doesn't rust, lighter when empty, and you can see the fuel level easily
Another consideration with the composite tanks is that they are shaped differently, and your current bracket/hold-down may or may not work on them. Also, I don't believe the upper rim provides the same strength (if your straps attach there).
Aluminum is usually shaped like steel so the fit is the same.
I'm not advocating for -- or against -- any type of tank; just nice to have more data going into the decision (I found this out when I was looking for a new tank to replace my steel one with the old style valve).
Raya
PS: I agree that the issue of getting them filled has probably become minimal these days. After all, they make composite tanks for forklifts now, so they are no longer an exotic. At one point in time I read that the last state that might have had issues was.... maybe Louisiana? That may not be accurate, as I'm going on memory, but the upshot was that it was the exception.