A long sanding block built to receive belt sander belts is a nice shop accessory. And you’ll use it more often than you think.
To make one, hook the belt over a 2×4, stretch it out straight and mark the length.
Cut the 2×4 to length and nip off all four corners at 45-degree angles.
Try fitting the belt. If you have to struggle to get the belt slipped on, shorten the block or make the 45-degree chamfers a little deeper. Too short? Start over!