I'm considering building an electric-gas hybrid using one or perhaps two hub motors driving off batteries and using a gas engine driving an alternator to charge the batteries. My question; Since the gas engine is not driving the wheels, is the size limit on gas engines applicable? I might mount the gas engine-generator on a trailer, only hooking it up for longer trips than the batteries would last on their own. It seems to me that since the gas engine is not involved in actually driving the wheels, it's nobody's business what size engine I use to recharge the batteries. The legality of using a gas engine larger than the law allows for a MB, if it is used only for recharging the batteries, is what I am asking opinions about.