Build a box with removable walls

[Frippegubben]

I don't know if I'm asking in the right place, but I need to make a box out of plywood and I want the long sides to be removable!

Shape-wise, think of it like a wheelbarrow, with slightly outward sloping sides, no lid.
Now I want to be able to remove the long sides in an easy way and at the same time, I want them to sit firmly when they are in place. The short sides and the bottom will be supported by a steel frame, so they stay as they should even without the long sides.

I'm thinking about maybe using a couple of those trailer latches to hold them in place, but then something more would be needed to align it properly so it doesn't slide around, if you know what I mean. Is there something smart I should look for in the hardware store to solve my problem?
And I don't want anything sharp sticking out from the box that could cause injury when the long sides are not in place.

Ideas, anyone?

 

[Sister ray]

There are probably hundreds of ways to do that. But can't you do it like on a regular trailer? There you often have hook hinges that, together with the flatbed locks, make it stable. But then one part of the hinges sticks out a bit when the sides are removed...

 

[Frippegubben]

These are protruding parts that I would preferably avoid...