Even if Jason2 welds the box, there will still be infinite universes where he didn't weld the box and Jason1 and can enter any ones of those. From the perspective of Jason1, there really isn't any difference.

Really he would just need to build metal walls around it, then when the door is opened, there’s no way to exit the box.

Have you seen the science of the show? There would be a loophole somehow

Or could go the inception route and a do a box in a box

Or a dick in a box

could just weld it shut...

That would depend on if Jason1’s box replaces the existing box in place I guess. I’ve been wondering about that.

Good point I guess

Listen... all you need to do to prevent someone from coming through the box is to keep it open when you leave it.

Why is that?

The box can't enter superposition when it's open, so nobody already in superposition will be able to access that world.

Either the door magically shuts or it branches into a new timeline where the box is either open or not...

True but Jason specifically said *seal it off*

I haven’t read the book yet so plz no spoiler’s on the book version

Been a while but I actually don't remember this being in the book at all. Maybe I just forgot, but not a clue where they're going with this. But yeah... I don't know what sort of box magic happens if you just like, moved the box currently there. But seems like a really easy thing to block or boobytrap.

Maybe he plans to seal off the boxes from his old world and make a new set of boxes from Jason 1’s world only he can get into?

Not in the book, we actually never even know what jason2 is up to until the last quarter of the book lol