I mounted my sliding rear tray bracket to the bike frames top tubes between the seat and the handlebars by welding 4 small aluminum tabs aligned with the brackets 4 mounting bolts, then using long stainless thru bolts to attach the tray. The battery slides On/Off the tray only when I remove the seat post, as it slides backwards to come off. It is just narrow enough to fit between my knees while riding, but if your doing extreme jumps and crashes etc, it may not be for you. A rear seatpost clamp type carrier rack could be used, but would need to be drilled out with a center bolt to keep it from swinging around behind you with that much weight. On a hard wipe out you might break that bolt, so use a soft bolt, so it will break rather than bend the frame or break the seat post. Just like a " shear pin" does on the propeller of an outboard motor prop. Carry spare bolt. I tried to send a pic but no room on this thread.