If you have a long-bed truck, the absolute best solution I believe is to bolt a receiver setup to the pin-box and front-mount a carrier over the bed of the truck in front of the trailer. I've been running that for several years now with over ~10k miles with a Swagman 4-bike rack. The bikes do not bounce, you can see them in the mirror, they don't extend the length of the trailer, and they clear the back of the cab with no problem at all. It's a great use of otherwise wasted space.
Downsides are limited to: The bikes accumulate more bugs and dirt (being in the wind-stream), you likely need a step stool to get them on and off, and you can't get to them with the trailer connected to the truck. All in all, minor trade-offs.
I made up the adapter by cutting and welding a receiver tube (at the appropriate pin-box angle) to a steel plate, with a brace, then bolted the plate to the pin-box. Works great, and the rack is easy to remove it you want to use it on the truck while the trailer is parked.