Yes, the truck's alternator makes enough power to run the fridge and keep the batteries charged.
I bought 2-gauge jumper cables from Lowes, it was the cheapest way to get 16-foot lengths of 2-gauge wire (gotta think outside the ol' box sometimes!). I cut the clamps off and made my own lugs from a small piece of copper plumbing pipe.
Just cut yourself about an inch and a half of it, smash one end in a vise (even just a hammer will work) and drill a hole in it. I smash the cable in the other end in my vise and heat it with a torch and add solder.
The only other thing you need to run heavy cables from your truck battery to the camper is a high-current connector. The best ones are the ones made for plugging in jumper cables on service trucks.
If you want to get fancier, add a continuous duty solenoid, with the trigger wire connected to a source of +12V that is hot only when the key is on. Then, the camper only draws from the truck when it's running. I've used oil pressure switches for this too - that way it knows the motor is actually running and the key isn't just on.
You can use a manual battery cut-off switch too, but that requires remembering to use it.
