I've made a working prototype for the DC DC converter using a 

DCM4623xD2N17C8y7z chip. It has been set to charge the 12v system to 14volts. I've just added a 10k pot to adjust the output voltage between 12.6-14.4v depending if I want to maintain the lead acid battery, run the lights, or bulk charge it. I've designed and ordered a circuit board, so the next iteration will be cleaner, will use anderson style connectors for the 12v side, enable charging with a key-on signal and will feature LEDs for on and fault states. Additionally there will be an external pot, so I can play around with adjustments from the drivers seat.