There are many ways you can change the rear of your car to make it in to a perfect transport for your dog or cat.  There are also various types of vehicles that are very accommodating to traveling with pets. 

Vans are a good vehicle to transport pets, especially on long trips.  Many people enclose the back of their van by installing custom upholstery and special air vents.  Or there are many kits you can buy to section off the back of your vehicle to allow pets to be out of their kennels but not have access to the front where danger of interfering with the driver is possible. 

Traveling in cooler areas of the U.S. gives the truck with a cover on the back a real possibility.  Sliding windows can be installed so you can still have verbal contact with your pet while traveling and a mesh covering prevents your dog from being able to get out of the vehicle while it's moving.  It's best to have them in kennels where they are more safe.

If you don't like to keep your dog in a crate, you can purchase a rubber bed liner that will make it more comfortable for your dog to lay on while in the back of a pickup.  These usually run about $50.00 and can be purchased at the same places that install camper shells.

There are a number of products you can order on-line to protect your car from any mess your pooch might make. Seat covers are very popular for the back seat for those that like to have their pet sit in the back on a trip.  Also, there is a long list of first aid kits that will make you prepared for any emergency with your pet while on the road.  Another thing to consider is the clean-up at the rest area's that your pet will be using to urinate and do number two.  Bring along a scoop just in case it is required in the area you use for this purpose.

The best thing to do is to get a gear bag to keep all your pets' food, bowls, first aid kit and anything else you can think of.  Then simply keep this bag with you where ever you go and you'll always be prepared for whatever may come up.  When not traveling, keep the bag in a special place already stocked with everything you need for travel with the exception of the food or treats. They may go bad in between trips.

The best thing you can bring with you on a road trip with your dog, besides your gear bag, is some kind of kennel.  There is a wide variety to choose from.  Soft-sided kennels are excellent for travel as they fold up flat when not in use.  There are also wire cages which allow your dog to see out so he can almost feel like he's not really in a kennel at all.  Then there are the hard plastic kennels with a minimal view for your dog.  Place a blanket over the top and he will feel like he's in a den situation.  Every dog and its owner has their individual preferences on what's best for them, but I high recommend keeping your pet in a kennel versus leaving the in an open car situation.