I have used 2 different truck extensively to charge trailer batteries.
#1 was a Toyota with the 400watt inverter, maxed out into a 15amp smart charger it worked excellent, and I would run the truck 1/2 the time, and let the inverter steal power from the truck battery the rest of the time. Cheap and relatively efficient with a high output alternator. Inverter and smart charger basically assured efficiency. I was able to charge my trailer batteries in no gen areas, an no one was the wiser.
#2 is my latest setup, 2011, and now 2013 f150 with the 220 amp alternator. I use all a few different options to draw power. One is heavy gauge cables from the battery posts. The alternator has such high output at low rpm, I was able to run our window AC off of it (via our hard wired inverter)all night, burning about 2ltrs an hour of fuel. It filled in nicely at 8000' when our little gen couldn't run the AC.
Long story short, I prefer not having to deal with carrying our generator with us, especially when the truck has vastly more output potential, especially at altitude. It works well, as long as you have an understanding about current flow, and find ways to make it run efficiently. Not to mention, no need to gas up middle of the night!
Happy trails!
