I am now able to fit the back panel into the cupboard and connect up the gas. I used 5/16” copper pipe which is the standard for caravans and campers. The pipe goes to the ball valve and then connects from there to the underside of the hob units. I used compression fittings at all the joints which are much easier to assemble (although prone to working loose if bashed about too much). Also when using compression fittings, make sure that copper olives are fitted – not the brass ones which are often supplied with the joints.
You can also see that I have fitted flexible tube inside the gas locker and further secured this tube using jubilee clips. When one gas cylinder runs out, all I need to do is take the regulator off the cylinder and fit it to the top of the other. The gas locker has also been painted silver.
On the other side of the back panel the waste water pipe has been connected up to the plug hole of the sink. This then runs down the back of the cupboard and out of the hole in the floor to the external waste water tank.