There's a siphon tube that runs to the bottom corner of the tank to pick up the LP... with the alignment hole in the tank facing straight down, this angles the tube to draw every last bit of the LPG.
I suppose as long as you make sure the pin and the vale is oriented correctly, that a sideways mount can work well, but you do run the risk of starving it on a side hill, vs. having to be pointed downhill, which i more rarely find myself sitting on.
If the tube thing doesn't make sense, I can try and find a drawing of the internals of a tank...
I forgot about the 4WS... I'd still put them as far out as possible, and vertical on the C is fine, unless you are planning on wheels with alot of backspacing??
