I have a Dee-Zee cargo carrier purchased from TSC - Tractor Supply Company - that we've used on our Outback for several years now. This year we bought an adult tricycle and wanted to bring it with us. Well, creativity and ingenuity prevailed. I took the sides off and made my own holder. At the time I did this, it was suppose to be just a quick and dirty attempt to slap something together. So I used old lumber laying outside. It was never intended to be a permanent fix. And actually, it's become a permanent solution. I suppose until the wood rots, I'll just keep using it this way.
Fyi, one thing you REALLY need to figure out, you may get one of those carriers with the attached ramp, but how wide are they... really?
My Schwinn Tricycle turned out to be much wider than the carrier, which resulted in the following design.
Before:
After we got the tricycle, this is how I modified the carrier.
Granted, I have to lift the tricycle up to get it on the carrier, but that's not too much of a problem.
The thing I had to figure out with the carrier when I originally purchased it was to stop the side to side rocking, which I'm sure would have eventually broken something. I built 2 supports (with 2x4's) under the carrier, and they actually rest on top of the bumper, preventing any rocking. It's stable.
Someday, I'll remove all that wood, and make the supports that hold the wheels out of PVC pipe or aluminum pipe. .... someday!