Adding a interior to wagons

[Kaldo]

The only problem I can see is if someone uses it to transport wood, since you could place an infinite amount of logs inside.

[SacreDoom]

The only problem I can see is if someone uses it to transport wood, since you could place an infinite amount of logs inside.

That's true, making carts completely useless.
Maybe if you couldn't bring things in there from outside the wagon, but had to build em? Like a cave with cattle and carts, etc. you can't take things out of it, you can't bring things into it.