I bought a "Safefill" lightweight cylinder two years ago. They are available in different sizes.
They are the proper refillable fibreglass cylinders (80% max.) The only problem was when I brought it to the local Flogas station they said they could not refill cylinders. I contacted Flogas giving them specifications etc. and eventually after about two months they replied "no".
To solve the problem I purchased an external filling adaptor and installed it on outer part of motorhome side, beside the gas door and fitted it - simple job. I then had to connect the internal part of adaptor to cylinder for refilling. I did this by getting a short length of hydraulic hose (High pressure), fitted a stop valve near end that attaches to cylinder (to stop escape of gas from pipe when switching back regulator to cylinder).
To fill all I do is disconnect normal propane regulator and attach the end of pipe instead, then open cylinder and valve and fill away. The same filling station that I first visited had no problem in filling from the outside. The cost of filling from empty is usually about €16.00 - much cheaper than conventional cylinder and the side is transparent so that you can see the remaining contents.
Details of these cylinders can be found on:
http://www.safefill.co.uk/pdf/…s-0217.pdf
I bought from the Netherlands as they were much cheaper than UK division and carriage was c €10.