I agree on the gasifier in driveing compartment. No problem about the gas leaks when we talk about charcoal gasifiers, but for a long range car, its hard to maintain the heat from the hopper to not damage the interior.
If l wuld make a charcoal powered car once agen, l wuld go with a towbar mounted gasifier and a small engine.
As for the gasifier being in to the motor compartment, it wuld sure be inovative, but 20l realy isnt much. 20l is preety much the volume of the reaction zone from a gasifier of a this size engine, so there isnt many room left for the fuel it self.
Try it and report!