Thread: Fixing a square box with warped wood (gallery inside)

I am building a box that sits on top of a freezer. The purpose is to increase the height of the freezer so kegs for home brew can sit inside it. Something like this
The problem is, I have this great old wood from my grandpa, but it's warped! The worst culprit is the front piece. When I clamp it together, it pushes everything out of whack and no longer sits flush on the freezer (which is important to keep a good seal).

Link to pictures: https://www.yogile.c...e/?vsc=883b8c0f

What is the best way to fix this? I can think of two different ways, but not sure if I'm missing something.

1. Sand the side piece a bit like this: /
   This is so it fits snugly into the warped front piece. This will make it a bit short at the back, but that side is against the wall so it doesn't matter too much.
   I would also need to use a bit of gap filler here and there, which, again, I don't mind too much.
2. Join it all together, even though it is out of whack, and then take a belt sander to it to level it all out.

Does anyone have any idea the best way to fix this?