Well... If you are interested in the idea of not having to charge your RC batteries, it would be very easy to hook up a small generator to the driveline somewhere. Mabe belt driven off the center driveshaft or right off the engine opposite your spur gears. it would function exactly like an alternator on a fullsize vehicle. The only problem that I can forsee is overcharging. So, you would need a mini voltage regulator or something in line with the generator to limit the generator output. Or simply put a tiny voltmeter on your RC so you can see it and when the battery is low just engage the generator witha switch or something. You could even do it remotely with a micro servo and a 3 channel radio.
It would take a tiny bit of power away form your RC though. But on a 300 HP truck running 2 batteries it takes about 1 HP so thats like 1/3 percent. I'm not sure where you would get the hardware for this, I just thought of it. But now i may end up having to give it a try.lol