There are two main issues I see, and you are probably aware of them.
1 Series hybrid (especially DIY) is probably going to be lossy, good chance that you will be farther ahead in terms of fuel consumption driving what you have.
2 You need a large motor, i.e. the transwarp should suffice, but you also need a large generator and engine if you wish to mostly eliminate the batteries and have a recognizable amount of power.
To try to get a handle on how much generator you need, I looked at an existing 150 converted to electric:
James Mannett's 2002 Ford F150
It uses 350 Wh/Mile (I guess)
144 volt system
500 amp controller
~40 mile range.
Weighs 5600 lbs with 24 batteries. And has power steering and brakes and stuff.
Since you are looking at the warp9, I took a look at that, it appears to handle ~500 amps for about 5 minutes, 300 continuous. Saw someone mention a 100kw run on a trans9, so that is 134 horsepower for best reliable performance expectation, ~3000 rpm (~150V) and 667A for short duration.
So for best sustained performance from the warp9 then, you would need a diesel generator that is at least 134 horsepower after the losses of mechanical to electrical, and the controller (and rectification?).
So now we have a couple real numbers to work with at least, to get in the ballpark, or at least have an upper limit on your power requerements.
A quick look at ebay, the cheapest 100kw generator is $4000,
Continental Diesel 150 HP 6 Cylinder Consolidated GE 100KW Genset Generator Used | eBay
It looks really big and heavy, and even used it costs about as much as batteries, but it looks pretty modular
And it is likely to use even more fuel than its non electric counterpart.
I will go out on a limb here and say I hate your idea, sorry bro. Spend the money on batteries if you are bent. Also consider scaling down to something more personal transport sized if possible.