Re: box joint separating
If you can force some glue into the joint before Mike’s suggestion it would be a permanent fix. It does not have to be fancy, spread the joint (scrap wedge or chisel), put a bead of glue on it, push in with finger, repeat. Take the pilot holes pretty shallow if you are using a 1/8” pilot bit for drywall screws. Short deck screws are designed for the outdoors and the square heads are the greatest thing they have invented in the last 10 yrs.
“Why do we fall, sir? So that we might learn to pick ourselves up” Alfred Pennyworth Batman Begins (2005)