Fit the narrower of the two into the wider section and secure them together with some cord, if you make the cord the right length(3" or slightly less) you can reuse it to tie them together later to keep the bottom half from dropping down the tree if it slips. Most tree stand mfrs sell backpack straps that clip on to the stand in some way, they aren't expensive. Get padded ones, trust me. In a pinch you could buy two padded rifle slings and use them as pack straps.