The gas locker on our van is designed to take 2x6kg bottles. On average a bottle lasts us over a year so theoretically a 3.9kg bottle will last 8 months which I have decided I can live with.
This provides 2 plus points:
1. The difference in the weight of the gas with the steel bottles x 2 saves me approx 12kg on total van weight (a lot when sailing close to the wind).
2. A lot of additional storage space for buckets and things I would rather not have inside the van – see photo.
Food for Thought!