Kirby, So simply and effective. Great idea.
I have been shooting off the hood of my truck and have made a variety of bags, even used a bipod ONCE (bounced too much).
I now have my 'solution'. Uncle Mike's Bull bag. Filled with sand, this thing is about 25 - 30lbs. Even grips the stock quite firmly. Only works with sporter/varmint hunting rifles.
The big cannons, I still shoot from my portable bench (Black and Decker Workmate with a piece of plywood bolted as a table - folds up, really very stable, and the right height)
so far, shooting it has proven as good as any other method used in the past. With a bit of practise, this should be the best for what I do. Big plus is there is no bounce!!!
I just put a pad under the bag so that I don't scratch up the hood. I have a canopy on the back so your idea will not work for me.
Another simple solution to LR field shooting.
Jerry