OP, I totally get wanting your own rig and will offer you advice on the premise that you will be going that route.
I own both a stock trailer gooseneck, as well as a 3 horse slant with a LQ. I haul locally with the stock trailer, but prefer the LQ trailer if I am going any distance.
The stock trailer is great for loading loading and unloading horses I don’t know. I feel like it is the safest option for me, as the layout offers the most options to keep me safe. My stock trailer is 16’ on the floor with a full swinging center divider with a sliding door in it. The rear swinging door is the same set up. I also have a full escape door in the front compartment on the passenger side, so I can get in and out of this trailer safely from the rear and the side. The gooseneck has a calf gate, so I can store things up there, but it is not as convenient as a dressing room. I love this trailer for hauling out to trail rider rom home, as I can haul tacked up and not worry about my horses getting hung up on something. This trailer is also as versatile as I can haul just about anything on it- hay, shavings, four wheelers, garden tractor and loader, furniture- you get the idea. This is a trailer we would not want to be without on our farm. It is one of the best purchases we ever made. Ours is an all aluminum 1999 Featherlite that we picked up about 7 years ago for only $6500, so it was a steal.
We prefer to use the LQ trailer for any distances because we feel like the horses are safer in it. This is something people will debate, but here is my reasoning. In the slant configuration, the horses are confined to a smaller area, yet still able to stand in a position that makes them comfortable while being hauled. Our LQ has mats on the side walls in addition to the floor, as well as windows that can be closed in the event of bad weather. And yes, I have hauled through violent thunderstorms, as well as snow and hail.
With a three horse slant, you can always remove a divider or pin it open, so your bad hauler has a little more space to get comfortable since you are only hauling two horses. When I camp, and usually take one or two horses with me, my third stall acts as my mud room and I store hay there as well. My camp kitchen is also stored in there, as well other miscellaneous things. It stays dry and secure with a half stud divider on the bottom half.
Have a road side assistance program like US Rider. Expect that if you have an emergency, it can be a couple hours before someone can get out to you. If they get there quicker, great! If not, your expectations are realistic.
Put the best quality tires on the trailer you can afford to, and make sure if you buy a used trailer that the tires are less than 5 years old or that you budget to replace them. Buy a tire that is speed rate for more than 65 MPH, as many speed limits are more than that, and even if you try to keep your speed are 65 MPH, you might need to speed up at times. Most trailer tires are only speed rated to that, so do your due diligence when tire shopping. Have a spare or two, already mounted on a wheel. This will save you tons of time and headache if you do have a flat.
Use a trucker’s GPS or app like Trucker Path, that can be downloaded for free. I have both, as well as a hard copy of a trucker’s atlas.
Have both your truck and trailer gone over for both safety and maintenance issues before you travel.
Have a basic emergency tool box in the truck- basic tools, emergency triangles and roadside flares. I also carry a fire extinguisher in my truck, as well as one in the LQ of the trailer. I always carry potable water for the horses, as well as a supply of several days of hay as well.
Map out your travel plan and have overnight stops planned and set and set up ahead of time. Confirm reservations before you hit the road.
Drive as far as you are comfortable with minimal stops. I have done as much as 900 miles in a 16 hour day, stopping only for diesel and bathroom breaks. I do not unload horses, and offer water when I stop, but my horses rarely, if ever, drink. They do drink well when we off load though.
Drive defensively, and if you have the chance to take a defensive driving course, which can be done online, do it.