I, for one, appreciate your post, Yaj. One thing about internet forums is that threads seem to drift all over the place until, at times, get so off topic that they result in arguments that sometimes have nothing whatsoever with the subject matter of the opening post.
Let's remember that the OP is asking about a lightweight pickup to tow behind a Class C motorhome. He obviously won't be interested at all, I'd assume, in towing a trailer that could house a pickup truck behind a Class C.
With that said, the new Ranger isn't yet available and even when it is, we've heard that it won't be extremely lightweight. A good used one might be a vehicle to consider, however.
Pertaining to 4-down vs. using a tow dolly, just about all our friends and acquaintances who have previously used a tow dolly and switched to a vehicle that they can tow 4-down, have expressed that towing 4-down is less hassle and are glad they no longer have to use a dolly. Sure, there are some who love using a dolly but they are in the minority.
Using a dolly may pose problems with towing a pickup too depending on the configuration where you may have to disconnect the driveshaft, tow it backward (?), etc. And if weight is a concern, which is assumed if using a Class C, then you're just adding more weight by using a dolly.
Our first response was based on what late model small pickups were the lightest and easiest to tow 4-down. The Colorado/Canyon is, in our opinion, the best combination of everything you're looking for. It's relatively lightweight (under 4,000 pound curb weight), it's 4x4, and there aren't any restrictions on towing or special procedures to follow.
Again, and this is only our opinion we are expressing, using a tow dolly is a hassle! Not only in the procedural issues but also the fact that you have a bulky piece of equipment to store both at home and at a campground. The initial cost may be more to install base plates, buy a tow bar, do additional wiring for lights, and buying a braking system but well worth it for most of us.
The advantage of a dolly is that you might be able to use it to tow another car or vehicle as opposed to a system that is dedicated to one vehicle.
I've attached the 2012 MotorHome Magazine dinghy roudup below if you'd like to take a look at it. It will give you the vehicles whose manufactures give explicit permission to tow 4-down. It is, of course, not a comprehensive list as some manufacturers choose to keep quiet about towing 4-down but some their vehicles can be towed nonetheless. As was pointed out previously, go to the Remco site for a comprehensive description of vehicles.