One suggestion is to use heavy gauge cables to the battery disconnect switch, and make sure to not have it any more than a couple of feet away from the batteries. Be careful when installing this and don't even for a split second let any wires touch the frame, or you're likely to blow the fuses in your converter (don't ask me how I know this).
Our disconnect is a very heavy-duty marine grade switch, on the positive side. It covers the entire + from the battery to the trailer. I don't really think that's a concern as there is no way we could hook up to the truck without flipping the switch, as our front jacks wouldn't work with it off. The switch heavily clicks into the on position, and I don't believe any amount of bumping around during travel could change its position.
Before we installed the switch, our batteries were slowly draining while the unit was in storage, because some things were still drawing power (propane alarm, etc). Now, we always have a fully charged battery when we pick up from storage.
Chris