Tecker, I have began to assemble hho cells also. It looks promising. I have a Ford Vic 4.6L (retired double knot spy car). Bought it at a auction 6 years ago. It gets a solid 20 mpg without it. I've heard up to 30% increase in fuel mileage with it. I'll see.
I can't find anywhere to mount the unit under the hood, but the trunk has enough room to be used as a camping tent in wet weather. That's where I'll mount the rig.
Good luck and keep us posted.
Phil