Hi Kebeck12,
I’m sure some others will chime in but looking at your sled rack one idea that comes to mind would be to first cut your auger rack off. Put it up front depending on your bumper or add something to the monster box to carry the auger or use the otter auger tube.
To mount the box I’d begin with 2 pieces of square tubing mounted either crossways or length wise on your rear rack. You can do this with u-bolts. The otter box can then be attached to the tubing with the included u-bolts in the same manner it would be bolted to an ATV rack.
You could also lose the rack and 2 up seat and mount it on the tunnel of the sled. It’ll sit a bit higher then the seat and act as a back rest for the passenger. Not as comfy as a 2-up seat but thats how I have it mounted to my sled.