Dead battery issue

An ammeter hooked up when key is off will show if something is still drawing.

 

You either still have a draw or batts are junk . New dont matter, could have a bad cell in one.

 

Check the alternator. If the alternator is warm to the touch in the morning before you start it, then the alternator is drawing the current. Had this happen to me once.

 

Does it have the built in frig. if so you will have to go inside it and turn it off every time you shut truck off?

 

So the relay the energises the field was stuck?

 

Check the lights that are underneath your bunk inside the side doors one of them may be staying on, I had that problem I did not realize it there was a switch on it I assume the light went out as soon as I close the side box door.
That is enough of a drawer to kill a battery overnight, especially if they're still incandescent bulbs and not LED lights.
Another issue could be batteries could be brand new did you clean your battery terminals with sandpaper a wire brush the part that actually connects to the battery your wires?

 

Do you have a power inverter?
My batteries will drain within 2 days of I leave it on while I'm home.
- check to see if you left a light on in the belly box under your bunk.
If that doesn't solve the problem, take it to your car mechanic (unless you can do it yourself)
turn everything off
Open fuse box
Check voltage draw on every single circuit
Some will be powered no matter what
Eventually, you'll find a circuit pulling power that shouldn't be
Like the light under my sleeper, it has its own switch but was powered up (under bunk lights are easy to miss cause when you lift the bunk they automatically come on and when you open the belly box... Yep... They automatically come on) ... Thats how you find the problem
On the cover for the fuse panel should be the "key" telling you what every fuse controls.