How easy is it?, I've just broken or rather smashed my own record? a gas/electric model out and on the bench, down from 7.5 minutes to 6 minutes dead!
John though is correct in what he says, so first disconnect the gas bottle, now don't reconnect it or allow anyone else to, until the cascade is back in and competently checked for a gas tight joint.
Also with mains hookup disconnected, remove fuse from Cascades mains electric heating switch and store out of the way safely
You can now use a 17mm spanner to undue the gas joint nut, then once outer flue cover is removed, take out 9 screws holding the heater to the van, COUNT THEM to make sure their all out.
With two large screwdrivers or better still two 1/2inch chisels, and a thin strip of wood to protect the van, starting on the bottom edge, lever the cascades mastic joint free and draw the heater out a few inches.
Go inside now and you can tilt the heater up so you can disconnect the mains electrical connections with ease.
Go back outside and if hose pipe cut off just past the connection, this is easiest and leaves a fresh end of hose when you put it back in.
Finally draw the heater out a little further and disconnect the gas burner modules plug connection and your done.