If the flexing is from the ground up through the entire support assembly, then I am going with a little heavier material than most commercial models and hoping that will stiffen everything there. I am also going to put leveling adjustments in that will be sturdy as well.
I am not sure where exactly mine flexes, guess I need someone to watch as I shoot to tell me if it's coming from the base or from the top. It does have leveling adjustments, they are at the base.
I think a separate chair would be more stable too. My chair is attached to the vertical post just above the base. But the benefit is that it's adjustable side-side and up-down.
Thanks for the input. Also how do you like the overall height of your bench? Pretty well all of us ar from 5' 10" to 6' 2". My son in law and nephews are 190 pounders and we go up to 245 for me, and maybe a little more for another friend. Do you have any input on how you would shape the notch at the back and would you let the bench extend further forward for more front rest room?
Overall height is ok, but for me, the seat needs to be at the lowest point or I don't have enough room at the front of the bench. Actually, I would rather lean forward into the bench then sideways against it, but the top is a little short (post to front) for this. So yes, I would allow more front rest room.
Some of the best groups I've ever shot (sub 1/4 moa) were actually shot from the hood of a pickup truck on a sandbag platform (4 or 5 bags on front, 1 or 2 on the rear). I leaned forward against the vehicle and into the gun from the rear, rather than from the side this way. Problem with the newer vehicles however is that the hoods slope more and it's hard to keep the rifle from canting in recoil due to the bags being angled down on one side.
The notch in mine could be more rounded, as it is, it's nearly a 90. But that doesn't really bother me much.