No, I've converted over 800 Elgrands fitting a 93L tank outside underneath in the spare wheel location, including
@Parentalnightmare 's Elgrand.
It is unlikely your LPG tank is as small as 30L but it might only hold say 50L depending on which firm converted it.
On my own Elgrand I have a 95L tank underneath in the spare wheel location and have fitted the option to be able to easily add or remove a 2nd tank that is carried inside behind the rear row seats. I currently have a 2nd tank fitted behind the rear row seats (easy to remove if I want, it connects to the system using quick fit connecters), this additional tank holds 80 litres... So I can have 170 litres of LPG on board, which is great if I want to tow the big caravan or boat over 400 miles at 70mph at 14mpg without using any petrol and without needing to refuel with LPG.
I usually refuel my Elgrand with LPG at home from a red gas bottle (catering size 47kg holds 92.1 litres) using the pumps I make and sell. The bottled gas costs me around 86p per litre and it's handy because I never have to visit a forecourt and the gas is delivered to me included in that price.