Good luck... I wouldn't do it as this breaks rule #1 - "Never mess with the truck systems. This is the only way to get home..."
Depending on your DC current demand by how large your battery bank is you could easily demand an additional 50-100 DC AMPS from your truck alternator system during the charge cycle and this may be over what the truck alternator can produce. That could result in "game over" for the truck alternator.. My 255AH battery bank will demand around 53AMPS DC current when first hit with 14.4VDC. This starts tapering back and in 30 minutes or so it will be down to around 8AMPS DC CURRENT.
Also idling your truck motor for three to four hours is probably not all that great on your truck motor.
I charge my 50% charge state trailer batteries with the on-board converter/charger being run by my 2kW Honda Generator setup using a RV30A-15A long adapter. This will get my batteries back up to their 90% charge state in around three hours of generator run time. Then I am good for the next day/night run off of the batteries.
Battery science says if your want to fully charge your batteries using 14.4VDC it will take right at 12 hours if you are able to produce 17-20AMPs of DC Current per battery in your bank...
Lets us know how you make out... Not saying it will not work out for you just something I would not put my truck alternator on the line. This alternator system is only designed to charge a single 12VDC START battery.
just saying
Roy Ken
