Thats a tough one. How well will the tank fill from the side?
If you put the fill on the side can you bring up a section above the top of the tank. That way its a better chance it will fill correctly.
I'd worry fuel will push out the fill or vent hose while your underway, and you can't put a vent too low as it just won't work.
You got some figuring to do, maybe a good shop can tell you straight.