Have you ever used a sliding ramp, like on a horse van? I don’t know anyone who doesn’t curse them each time it gets used. Ramps will hang up instead of sliding neatly into place, while you are STILL holding up all that weight. The least bit of “not perfectly clean or even” will affect how the ramp comes out or slides back into place. Sliding ramps are WORK, each and every use. Being good at cursing helps, sometimes they just won’t go back in place without some extremely creative cursing! Not obscenities, but descriptive cursing. Seen that work for the ramp person a few times, to get ramp loaded, slid into it’s space!!
I would get a trailer with a ramp, teach horse to enter and exit better with the ramp. I have used both step ups and ramps, would take the ramp over step up any day. Various models of ramps are easier and harder to put up, but STILL worth the momentary effort over hard work of a sliding ramp.
Cleats on the ramp help a silly or scared horse, giving hooves an anchor point instead of sliding on the matting. He gets confident hoof will stay put on the cleat when getting in or out, so they load better and better. Even with pouring rain, the cleat helps the horse on wet mat to keep his feet where he puts them to get in or out of the trailer.
The other point in favor of ramps, is horse CAN NOT slip his legs under the back lip of trailer to hurt himself. Sometimes footing under trailer rear is bad, muddy, rough, too low, so horse has a bad time getting his footing to enter or exit safely. I have seen hind legs get cut, wrenched, when hoof goes under that lip.
You buy a trailer for long term use. You probably will have it for years, with more than a single horse using it. I wouldn’t buy a special trailer for one horse, unless he was like Trigger, paid for it himself! Ha Ha. With some calm training, lots of practice, your horse should learn that good things wait inside the trailer. He will be calm, easy loading with the ramp, so you can load up and be off to enjoy things. Save the “special option” money for sliding ramp to buy other fun horse things, like a camera to watch him back there, some fans, a blanket with his name on it. You will still come out ahead of cost of the special ramp being made. AND you won’t have to deal with the various ramp issues of a slider.