[M_a_t_t]

The best handling conditions are when all 4 wheels have the same weight on them. I couldn't find the article I was reading on doing it diy, but its called corner balancing. I would imagine with motor, transmission, and (half?) the batteries in front it would be pretty front biased.

I would go for one of two things probably:
1. remove gas tank and put the batteries in its place, chargers in spare area

2. CUt a whole in the floor and put a box similar to this to gain access to them from inside, then put it all in there. If the gas tank and spare area are next to/ above and below each other.

However, I don't know exactly what the layout of your car is, but that is what I would go for.

Good luck