So I have been very entertained by this thread. I wanted to redirect it back to building a hybrid truck though.
I tow all the time. I know that the new Tundra hybrid is specifically to help with towing, not MPG, and the F-150 hybrid can tow, but anything under a 1/2 ton sized hybrid vehicle has abysmal tow ratings. Could you take the OP's idea of a mild hybrid add on build to aid in towing and MPG and not effect the overall tow rating of a factory ICE vehicle much? I know, I know, have my cake and eat it too.....
Here is some background to help you understand where Im coming from and trying to accomplish. I currently drive a Mazda CX-9 (i know, not the best tow vehicle, and likely not a great candidate for a hybrid conversion, but great driver's vehicle and family hauler), and have an order in for a Ford Maverick Ecoboost (not hybrid). I need a minimum of 3500lbs tow capacity for my tool trailer. I currently get about 13 MPG with the 2.5 T Mazda when towing, and about 25 MPG highway when not towing. I could switch to an F150 or similar, but would just get like 20MPG all the time. Would it be fesible to take something like the Maverick and add an inline electric motor to keep the 4k towing capability, but bump the MPG up? Or would a 48v motor/gen attached to the ICE motor be a better way to accomplish that goal?
edit- also, if there is a thread this should be in rather than this one, let me know!