Hi. I am waiting delivery of a Autotrail Expedition 66. In the next 3 weeks. I was told that the refillable 2 gas bottles were the 2.7 kgs each, because of the small space for them. I would like to fit at least a 30 litre tank slung underneath. Not sure yet if there is space for it. I was wondering if anyone had fitted a tank underneath, and what size it was. Thanks.