Options abound for sure with this Matt. If you’re dragging a tire or sled with a “normal” Denali sled amount of resistance then I will commonly have athletes rig their Denali backpack as if they were on the mountain and then use that sled haul webbing to pull the tire or sled. This allows them to carry a bit of weight in the pack and a slide at the same time and also gets them used to the exact way that the sled will be pulling on them in the field. Alternatively, I definitely have had folks use a climbing harness but the pack makes more sense in my mind. In general, the backpack has a loop of webbing and the tire or sled has a pull cord tied to it with the two joined via locking carabiner when you’re doing the sled drag. This is a good visual for what I mean
If you’re tire dragging then sometimes its best to drill a couple of holes in the tire and pass an 8-10′ piece of cord through the holes for the attachment. Hope that helps get you started!