Charging from your vehicle 7-way doesn't work very well, even if you have a high capacity alternator, and especially so if you really do have two 6 volt batteries! You definitely want another means to charge, either solar like @Newfisher mentioned or a generator. If you do have two 6 volt batteries and they are fully…
It sounds like you have two 6 volt batteries. That will give you considerably more capacity to run lights, etc. Get a plug in 12 volt meter to watch your charge. Make sure you are fully charged before you leave for your trip. 4 hours may not be adequate to recharge your battery depending on your depth of discharge.