1. Towing a vehicle behind an RV is no different for trucks than for cars. It's just weight, equipment, a the specific vehicles mechanical limitations, if any.
2. State laws vary, so some states require brakes at lower towed weights than others. If legality is your only concern, it's just weight, brakes and lights. If safety enters into your decision, let me assure you that any towed vehicle that has active braking will enable you to stop the rig in a much shorter distance than one without any braking. The more the towed vehicle weighs, the more having its own brakes will help.
The CA DMV says that any towed "trailer" weighing over 1500 pounds must have its own brakes. I can't find anything about requirements for independent brakes on a towed car or truck. Anyone know?
I don't understand your question. "must have its own brakes" seems clear enough. When the towing vehicle applies its brakes, the brakes on the towed vehicle also must be applied. There are various add-on devices that do this, some permanently installed and some portable. They all work adequately. Some popular auxiliary (towed vehicle) braking systems are Brake Buddy, RVI Brake, SMI Duo and Air Force 1, and Brakemaster.
Generally speaking, 4x4 pick-up trucks that have a neutral position in the 4x4 transfer case can be towed. The method of getting it into that neutral position varies by make & model, of course. 2x4 pick-ups may possibly be made towable with the addition of either a driveline disconnect or a tranny lube pump - see Remco Towing at http://www.remcotowing.com/Towing/Store.php