Charging while towing

I prefer to run my fridge on 12V while towing also. 

But when we ask a question or propose something on a forum, we all need to expect questions and challenges, otherwise why ask?  In this case the physics behind the energy flows is what it is, and it works the same for everyone.  

Of course its totally up to you what you do or don't do with information you get, its your rig. No argument from me. 

But if you attempt to charge the trailer battery from the tow vehicle battery you are merely moving energy from one battery to the other. It is a zero sum game, so completely different from using an external source. And the battery you are removing energy from has less capacity than the one you are moving it to. 

Lets try it this way.  Think in terms of energy flows. When you say you want to "top off" the trailer battery once you've parked, where is that energy coming from? Are you idling your tow vehicle and using the alternator to provide it? If so, just change the fridge over to propane and leave the 7 way connector attached. Problem solved. 

You can't charge from the tow vehicle without the alt running because that will remove energy from the TV battery and discharge it in short order.  If you are thinking that you can charge directly between the two batteries using the 7 way while at the same time charging via an inverter/charger in parallel that won't happen. The dc voltage will be established by the two batteries which are after all connected in parallel forming a single 12V buss.  The inverter/charger will just act like a load, basically a high tech heater sucking more energy from the system than its putting back in to the same buss its drawing from. You would have to disconnect the 12V connection between the two batteries and charge only through the inverter/charger. But why do that if you can charge directly far more efficiently just like you are doing while driving?

Since the Rpod's converter already has the capability of charging the battery while the vehicle is running, I have to assume your TV does not have a strong enough alternator to run it. The other option, as you are trying to do, is to use a smaller charger in hopes of it working.

There is a Auto-breaker up front on the Rpod and this is where I tapped in to run my inverter. Just follow the wiring back on the harness, you'll see it. This may be your spot to tie in.

Like others, I do believe you are better served not going DC/AC/DC and staying DC/DC. Pickup a smaller DC/DC unit that doesn't require as much input wattage. 

I'm not thrilled with turning off and on the propane everytime I fuel.  I have been able to run with the frig on DC for 9 hours with no issue while driving. The charger idea is more for if I want to do an overnight and don't have a AC hookup....I can top off the battery when I park. My Escape is already wired for 12 v in the rear of the car so it is just a matter of plugging in the converter and connecting to the battery.