I gave up on the slide idea as with curved Sprinter walls, the Lance straight slide would have to be red necked.
Than with rear dinette and camping in warm weather (with no mosquitos) I think opening rear doors 270 degrees will open lot of space behind dinette, where I can always add rear platform and roof sunscreen.
Also 1 of my goals is to keep "low profile" so beside roof vents and solars you won't be able to tell it is RV.
I will try to put water connection under fuel door and hide the 30Amp plug/cable under the body.
In the mean time I put ScanGauge on our sedan to check fuel consumption.
It show 0.83 GPH idling and 0.97 with AC at full blast.
Higher than I expected, but than ScanGauge was giving me false data in the past, so it has to be verified.