It really depends on what you want and need. For me, space and cost are a huge factor. I don’t have a lot of space. I started with using me foldable utility trailer that I use for my dirt bikes. Worked great, and I could set it up in less than 1/2 hr, but it was still kind of a pain. One race I took off one side of wheels and nerf bar and put it in back of my wife’s SUV (which a lot of people do this or put in back of truck).
Then I got to thinking that my buddy had one of those motorcycle carriers for his hitch. I thought that if this could be done for an upright motor that weighs much more, it should be easy for a kart that is low and flat. I starter looking for a pre manufactured one, and only found one that was well above $500. So i figured I would do something on my own. After all, the karts only weigh between 150-200 lbs.
I ended up buying a simple cargo carrier that has a 500lb wt limit and lining it with rubber hosing (so it doesn’t scratch my frame) and it works great. Feels like I have nothing back on my car.
Before when I had it on my trailer I would lock my kart to trailer and trailer to my car. I never worried too much about it over night, but I have only done it a couple times.