This forum had a lot of great advice on picking a trailer.
https://pinside.com/pinball/forum/topic/pin-hauler-trailer-discussion#post-4775584
I remember ibuypinballs (Pete) has a trailer that he brings to shows. He set up the e-track so that when he places an em or early solid state, one e-track secures the cabinet, and the other secures the head that is standing on top of the cabinet. The advantage of using an e-track system is that you can secure each game separately.
I use uhaul 5x8 trailers because they have the tallest interior height. One time I secured four pins on each side of the trailer using long ratchet straps. The straps that I used were strong enough for the total weight of the pins that I was hauling, but when I opened the trailer after a long drive, two of the cabinets had fallen over. Luckily no damage was done. If I ever buy an enclosed trailer it'll have a v-nose, have a tall enough interior height to haul pins with heads on top of cabinets, and standard height arcades.