Touring caravans are not certified to allow anything other than a MAX high pressure hose of 450mm.
The problems do not stop there, you may not be able to site a large cylinder outside the van depending on site rules.
If you are allowed, the cylinder must be sited on a firm level base and the cylinder secured so that it cannot be tampered with or fall over.
If you choose to ignore the legalities and fit longer hose that will be entirely at your own risk.
The longer hose MUST have swaged fittings, Jubilee clips are NOT permitted on high pressure hoses.
You will also run a much higher risk of regulator contamination due to the longer hose length.
I would very strongly suggest staying with what you have, it is legal, safely out of the way and you would be very unlikely to use two cylinders in less than 24 hours, so plenty of time to get replacements.