How will you know it's effective? If you don't wound one? Quite the price to pay for the deer. Caldwell and other companies make tripods, quad pods, you name it. There are shooting bags you could put on the window ledge. A couple crappy pieces of rubber seems to be the worst solution I...
You're making a couple hypothesis that may or may not be correct. It may have nothing to do with the stirrup, and it may not be string jumping, at all. What broadhead?
How far was the shot? You couldn't hear or see the bolt hit the deer? The deer could be brisket shot, gut shot, you name it, it could be a miss. If you do think it's gut shot, 4 hours isn't near enough.....
I fillet hundreds of fish every year, I don't have time for all of that, especially when I see no up-side. If you want to vac pac them, why flash freeze? Not everything has to be so complicated.....
Just fillet crappie and put them in a plastic bag. Cover them with water, then work the air out and seal. They stay good for a good long while. No need to reinvent the wheel, always.
You make everything so complex, something is bound to fail. Multiple connectors, switches, plugs (another connector), etc. I'd take a hard boat with a comfy seat any day...
Run the live off your trolling motor battery, or are you 24V? You may experience interference, you may not, in my experience. The odds of interference is less since it's not on the motor.
Not sure about Humminbird, but Garmin says not to zip-tie the transducer wire to the motor or pole, use electrical tape. Perhaps Humminbird protocol is different.