I think your last drawing looks pretty good, just 2 comments:
1) your drain position looks pretty inaccessible from the outside - I sometimes use mine to fill up a dog dish or something without having to enter the camper & turn on the pump. It's not real fast, but it works; this could also take the place of an outside hose if you're not looking for a pressurized line. If you wanted to do this, you could just run the drain hose over toward the side of the van, behind the wheel well near your pump hose, to be easier to access from outside.
Although in your case, you'd have to be inside to turn the valve. Nevermind.
2) if you want to be able to fill your fresh water tank from the city fill line, add a line with a valve from the city fill to the pump inlet (just bypass the pump with a valve in the bypass line). I'm planning on doing this sometime for some reason. It's not necessary since you can just put the hose or an adaptor down the gravity fill. :)
That's all I got.
CC