I ordered an aluminum RCI for my Jeep but that was more for space and design issues than a materials debate. If space wasn't an issue, I would have went with the poly. Aluminum looks really nice but it can crack. A puncture or leak in a poly cell is easily repaired, not so easy with the aluminum. T/fore, if you go alum., make sure and get one from a very reputable mfg. like RCI. Sump is a good idea for a 4x4. My aluminum doesn't have this so I went with Holley's multi-point pickup system so that no matter the angle, it won't starve for fuel. Most setups I've seen and researched that have a cell with a sump do route the sump through the floorpan like you've mentioned.