I see several problems.
First, I've been carrying supplies in a day pack that goes with the tree stand climber, for some twenty years. Both are carried in and out of the woods, every hunting day.
Long before hunting season, I worked out carrying the tree stand in the back yard. Better I found, to field test the tree stand before I needed it for hunting. The day pack is tied to the tree stand and put on my back, too.
To secure the two part climbing tree stand, I bought these small bungie cords from an auto store. Use two to tighten up my tree stand. They were big enough to just hold the two metal parts together.
I bought two inexpensive rifle sling straps for a tighter carry. These slings could work on a rifle or shotgun, but are not "made" for $900 rifles.
Two cushions, which I rehabed and came with the stand are repositioned to my "******" back.
The unknown factor. Getting in shape to carry a plus 20 lb. tree stand, a 10 lb. day pack, and a rifle or bow. With my rifle I estimate I'm carrying some 40 extra pounds. Add this to any excess pounds on your carcass, we're talking about some weight. Think ****** instead of hunter.
Practicing with the items before the season, may start to motivate you to walk every week and lift some some light weights. A hunter isn't suppose to be a couch potato. I'm afraid some think they can be.
Now out for my mile and a half hike.