I agree with what Native said. I'd only add that if you are using deep cycle lead acid batteries for your house batteries and charging them with the vehicle alternator their life span will be considerably shortened (per Trojan mfg). Furthermore, if you use all start batteries you will not get as much power over time before the start batteries have run out of available power.
A better solution to charging deep cycle house batteries is via a battery to battery charger. This allows you to use the alternator to charge all batteries in the correct way for their design and provide the greatest longevity for both types of batteries.
Whichever method you choose be certain that your vehicle's alternator produces enough power to meet your charging needs without having to run flat out 100% of the time--it'll fry your alternator. The rule of thumb I was taught a million years ago is that an alternator should not be tasked to run at over 85% load except in short bursts like when rapidly recharging the start battery after start up.
Jack