I bought my bike rack back in 1995 for $200.  Expensive, but worth it.  Unfortunately, the company is no longer in business, to the best of my knowledge.

Swagman makes a similar model.  Doesn't have all the features that mine does, but does still allow towing.

The key to this bike rack is that it slips over a drawbar.  A clamp then holds it tightly to the drawbar.

There's a bolt on that also helps hold the rack securely to the drawbar.

The rack has a security bar that drops over the top of the bike frames and is locked via a padlock.

The upper portion of the bike rack can also drop down to give more room when the bikes are removed.  I leave it up, which stops people from smacking their shins into the hitch!

Even when I add a second bike, they stay well clear of the trailer, even during the tightest turns.

A cool feature about my bike rack I haven't seen on other brands is the ability to tilt down, even with bikes still attached.  This allows access to hatchbacks and tailgates.

Another view of the tilt feature.

This rack was originally purchased for use on the back of a conversion van I owned.  With a few seconds, I can transfer it to almost any vehicle.

A last minute photo as we were headed out to Yellowstone.  This would be a 7,500 mile trip.

Parked in front of a frozen lake somewhere near Yellowstone.  The rig was grungy from the long haul, but the bike rack performed perfectly.

The first step was to find a suitable piece of metal to replace the bumper.  A friend gave me a piece of heavy duty aluminum that would work just fine.  Plenty of strength, but it was a little short.  Oh well, the price was right and it worked fine.

The next step was to purchase a bike rack from Camping World.  This was only about $30.  The nice part is that it can be quickly removed.

Oh, but I heard you can't put a rack on the back of a trailer!  While some may try to tell you otherwise, I've used both of these for a decade, traveling more than 20,000 miles without any issues, including the dreaded sway.  But it wasn't luck, it was careful planning.  In order to keep the trailer behaving itself, it's very important that the tongue weight be 10% of the trailer weight.  If you add weight to the back of the trailer, add weight to the front to balance it out.  Not rocket science.  Load the heavy items in your trailer forward of the axle.

The trailers that are very prone to sway are the ones with a storage box on the front.  Unless you load these very carefully, I'd suggest not attempting a bike rack on the back of the Popup.  They are already too light on the tongue weight, IMHO.

Here's the rack I purchased for the trailer.  Note that the stock mounting method is to use two clamps over a box type of bumper.

My upgraded bumper with the lower half of the bike rack posts bolted to the face of the bumper.

A side view shows that it will just clear the camper.

The upper half of the bike rack just slips into the lower half.

I put a bike on each of the two racks, and I'm ready to roll.

Another view.

Now you can see how the bike clears the camper.  The handlebars easily clear, and the peddle just misses the license plate.  The rack is so secure that the bikes never touched the camper in all those many miles.

I made sure that the bike was high enough not to drag a wheel if I drove through a ditch.