What’s your garage roof like? More and more, if they know the bikes are of value, they’re going in through the roof.
Garage doors are easily bent open. If you don’t keep a car in there I’d be tempted to brick the front up entirely and stick a window in it. Side door, mortice lock & wood… kick in door or crowbar, easy job for them. Consider replacing with full on house front door style with multi point lock. If you’ve got an internal door then breaking into the garage is effectively breaking into the house and will become a more serious crime for them than breaking into a shed or garage.
The box thing, can’t help you there. Except consider that the garage is a nice quiet, dry and safe place for them to work at their leisure.