Nevermind, i just saw one of your previous posts. Is the house battery just for charging while the van is turned off?
The house battery will provide power both when the van is running and when it's turned off. There is an isolator between the positive terminals of the house and vehicle batteries that prevent the house battery from drawing power from the vehicle when the voltage of the vehicle battery is below 14v or so. What this means is that power will only flow from the vehicle battery to the house battery when the vehicle is running and prevent the house battery from draining the vehicle battery.
My house battery is located under the driver's seat, along side the vehicle battery. Note that if you have a Transit and don't need/want a house battery that Ford has provided a fuse protected 60 amp power connection point at the rear of the driver's seat. I recommend you do a search on the
Ford Transit USA Forum for more ideas about house power to your van. You'll find references to solid grounding points that Ford has provided as well as recommendations on attachment points.
I do not have any hardwired provisions to charge the house battery with shore or solar power at this point. What I've found is that the house battery gets sufficiently charged for my needs during normal driving. I've also mounted my chargers and power strip on a removeable board so that I can easily take the chargers into the job site. I've also sometimes run an extension cord out to the vehicle to plug my charging station into. My set up is not really strong enough to charge two of the DeWalt FlexVolt batteries at the same time using the inverter. I've really not found that to be an issue.