stock tank with no pump, 26#
After modification 14# and everything works, gauge, sump and filler are still stock and work like stock. It has the original strap to hold it in place and all the weight is in the right rear corner where I wanted it. It holds a bit over 8 gallons but 4 gallons covers the sump top and slosh is kept to a minimum due to the size.

I cut the tank to the bottom and folded it up where the drop off at the pump top is. No welding within 6" of top to keep from warping where the O-ring is. Tig would be best but I only have mig so I did that and then brazed over the whole seam. Had no leaks the first time. You need to cut it in a straight line with the drop off to leave room for the gauge float.

It is just one more relatively easy/cheap alternative for an S13.