I pretty much used all the heavy objects I could possibly find. At first I put the weights on the sides but there was a little gap in the middle so I decided to move it all to there instead.
As you can see in the first and last pictures the gap is by the middle clamp, and it's quite small, about a millimeter or less. On the sides it's all fine, as you can see in the middle picture. I guess I will just add some more glue later and then sand it down, just to fill the hole. It is 100% sealed though, because the glue filled up nicely all the way on the inside. And if I want I could seal the entire cabinet from the inside later if I want to, but I guess there will be no need for that.