It only holds 2 bikes, but we use the Jack-It rack from Lippert. The kids bikes go inside the trailer for now, and I am looking at a ladder rack in the back to carry them instead of inside.
I find the Jack-It awkward to adjust for different bikes. It can be very difficult to get the bikes mounted up there. Some owners with trucks say the job becomes much easier when they can stand on a lowered tailgate, but I don't have a tailgate.
Overall, I like the use of that space and it works, it is secure. Not perfect though.
Not my photo, but looks just like this: