this is a question that has kept me up at night especially lately. This is a project I've been working on all week it started out at a competition. It was a p.i.t.a to get the cart and smoker on the trailer so I decided to go with a hitch mounted solution.
if you decide to use large casters keep in mind it will be top heavy I decided to lay my cart on its side while transporting as I did not feel comfortable with the car to being up right if you have a horse trainer it would be fine to put it up against a wall.
I would suggest a table lift for getting it on the trailer..harbor freight or norther tool
I did not feel comfortable with a hitch mounted solution but with a triple point hitch mount solution that
works for me here's a sneak peek
Hitch and cart upside down
Does that foo have 3 hitch points..yuuup