In the Spring and late Fall for 3-4 day trips I prefer the east coast
(on the Sea of Cortez). I've been beach camping near San Felipe for close
to 25 years. There are developed campgrounds (running water, showers,
flush toilets, palapas-palm thatch structures providing shade) both north
and south of town. More rustic camping can be had south of San Felipe
towards Puertocitos. A lot of Americans travel down here especially during
spring break (I avoid coming here during that period). This is beach camping
at its most basic. Nothing to do but read, eat, drink, swim, and bake.
Many people bring motorized vehicles which they drive on the beach. Further
from San Felipe the less of these you'll encounter. I've had the campgrounds
to myself some trips and on others they've filled up my second night there.
Generally, holidays are crowded. Less people early spring and late fall.
In the summer we'll head to the Pacific coast south of Ensenada and north of San Quintin. These are surf trips. There are about 200 miles of coastline with dozens of beaches. Most other campers will be surfers or kayakers with a few beachcombing enthusiasts sprinkled amongst them. I've never camped in a developed campground along this coast (although they may exist). This is truly camping at its most basic. You must bring all your supplies.
When we have a couple of weeks then we head as far south as possible. LA Bay, Guerrero Negro (San Ignacio Lagoon &Ojo de Liebre-the grey whale breeding and calving lagoons), Punta Chivato, Mulege &Bahia de Concepcion. These are on both sides of the peninsula. I've been as far as Cabo San Lucas but not for 20 years. To do it right you need 3 weeks. My wife still thinks of the Christmas trip in which we visited all the places mentioned above as her favorite vacation of all time.
As far as the vehicle is concerned you just want to make sure it is mechanically sound. Mexican auto insurance is important, of course. Usually we are with the vehicle but keep it secured when we're not. Baja, south of Ensenada is one of the most sparsely populated areas in the world and the potential for crime against your vehicle is pretty low. Myself and friends have experienced vehicle breakdowns in Baja. It definitely puts a crimp on the trip but also introduces you to Mexican ingenuity (as well as their different sense of urgency). So far I've never left a vehicle down there.
The dogs absolutely love it. I've been taking my various dogs down to Mexico since 1979. And that includes one pup that accompanied me all the way to the Guatemala border. This lucky girl got to climb the pyramids of Palenque and swim in the Carribean waters off Cozumel. Dogs must be vaccinated and you must carry proof of their vaccination and good health. These certificates are obtained from your vet and are necessary for your return into the States. But, frankly, I've never been asked for one by customs agents. In Baja, or the rest of Mexico, I've never been asked for any type of papers for my dogs. The usual precautions are necessary. Encounters with wild animals; rattlesnakes, raccoons, stingrays, and jellyfish. In San Felipe other campers will light off fireworks which can make your dog bolt. Mexican dogs aren't a problem. They are usually submissive to my dogs. But they'll quickly join your campsite if you feed them. My dogs usually make a few friends and hang out with them during our stay. The biggest problem is that the dogs will over do it. Sore pads from running too much in the sand. And diarhhea from swallowing too much seawater.
I've been traveling down there for many years. I speak Spanish fluently and feel quite at home throughout all of Mexico. But just like anywhere else there are people who prey on travelers. Also, there are many Americans that don't respect Mexican law and find themselves in trouble. Usually drug and/or alcohol related. But for thousands of Americans it is their favorite camping destination.
John Rule San Diego, CA