I use a 2003 Dodge dually with the powerful and reliable Cummins turbo diesel engine and a 2006 4Star all aluminum stock trailer.  I pull extensive maintenance before very trip.  My trailer is pictured here with the plexi-glass inserts installed for winter.  In the summer the inserts are removed for maximum ventilation.  Either way I have installed 6 roof vents for flexibility in maintaining a comfortable ride.

Here is the inside of the trailer set up and ready to go.  I can haul 6 average size horses with this configuration.  Hay and water are available at all times during the trip.  I have the cut gates open in this picture, but the floor to ceiling dividers allow me to haul stallions on the same trip with mares and weanlings.  Some of the longer coupled "jumper type" horses require a stall to themselves because of their length, but the  7'6" tall ceilings are adequate in height.  In fact I've hauled 18+hh Shires who required 2 stalls!  It's a pretty flexible set-up.

As you can see here, I can tie a horse off if I need to.  In fact, I placed lash rings so that I can tie/water/hay in 4 places per box stall.  12 places in all.  But, unless I have to tie a horse, I haul all horses loose.  This gives them the freedom to move around, stretch out or even lay down.  I have never seen a horse come off of my trailer stiff and "stocked up" with this set up, like can happen on a slant load trailer.  In fact, hauling horses loose staves off "shipping fever" as well as stiffness.  You can give a horse shipping fever in his/her barn stall.  The worst way to ship a horse is to tie his/her head up in a corner with a dusty hay bag in their face.  This doesn't allow your horse to clear his/her respiratory tract.  A horse has to lower his/her head and "sneeze" to clear fluid.  If left tied long enough, you can kill a horse as pnuemonia will set in. 

As you can see here, there is a full 1" thick rubber flooring under the pine shavings.  This flooring is more "spongy" than thinner more dense flooring options.  You can also see the floor to ceiling cut gates making 3 8' box stalls.  The divider gates have slider doors allowing me to move freely from stall to stall while checking the condition of my passengers and doing hay and water.  Yes, I can actually walk around and inspect each horse while doing hay/water, you can't do this with a slant load trailer.  I also have 4 interior lights and one rear load light, making nite time a breeze.

Up front, I've added extra gages to help monitor things under the hood.  I've also added on board GPS navigation to help me stay on the most direct route.  In addition, I've got a CB to stay up on local traffic and road conditions, believe it or not, this is the most effective tool that I have for real time travel info.  I know about accidents miles before I get there and can pick a route around major backups.  I've got an XM satellite radio for music, weather and news no matter where I am.  I've also got a laptop with wireless internet for keeping up on emails and again, weather.  You can't watch weather enough at certain times of the year.