I would not install diodes into the current wiring but instead install a totally separate wiring harness and a set of extra bulbs in the taillights. when you're hooked up to the MH the umbilical will use the separate wiring harness and bulbs. when driving the toad you'll use the mfg wiring harness and bulbs. we did this on our '03 Jeep Wrangler after multiple failures of diodes leaving us with no taillights or brake lights on the Wrangler. we now tow a 2010 Jeep Liberty that uses a separate wiring harness. no problems in the last 5-years.
if you don't need to leave the key in your ignition in the ON:UNLOCKED position you likely won't need a charge line as nothing will be on. our Liberty is towed with the txfr case in neutral, the tranny in park and no key in the ignition (steering wheel does not lock).
