Every conversion will experience losses as you have stated...
Unless somebody discovers some new method, its my understanding that...
"...One Amp for 4 sq inches of plate, any more and there is an exponential increase in electroplating/erosion, 1 amp for 6-8 sq in is better for long plate life, but if quality stainless steel is cheaply available, the higher amps will produce more HHO.
1.8-2.0 Volts per cell, any more and there is excessive heat and water vapor production...even 1.7V per cell, hardly can see bubbles flow out from cell. 1.8V and above the cell produces fair a mount of bubbles..."
This is from a guy using a 14V car alternator to power 7 stacked series cells (7 cells X 2.0V/each = 14V)
I haven't made one yet, but many websites show working devices. Based on real-world data, you will be VERY disappointed chaining that many conversions to power a wheel. Most I have seen used an alternator to generate enough gas to roughly displace about 10% of the gasoline.
If you are using the on-board battery to produce gas to power an engine to generate electricty for the wheel-motor...I am certain you will end up pushing your EV home after just a few miles.
IMHO, optimum configuration is light/aerodynamic two seat 3-wheel (two in front, 3-wh is technically a motorcycle) that uses only batteries. Pack would be lead/acid to start, later upgrade to half lead, half lithium. When longer trips are needed, a small series hybrid trailer can be attached using fuel of your choice (I like bio-diesel/WVO)
Just my $.02, best of luck!