Looking at many pivot benches that have been modified by removing the stool seat and adding a 'boat seat' with a back, I'd like to make others aware of a caveat by doing so.
By adding a seat with a back, it promotes leaning back. This can produce a very nasty situation if the shooter is leaning back while the seat is positioned between two bench legs and tips himself, his rifle, all his gear and the bench itself onto the ground. We saw this happen at a Portland gunshow, also in the field when we saw a guy shooting in the rat patch a few years ago with a modified seat on his bench.
As usual, the laws of physics are strictly enforced. So if anyone is considering adding a boat seat to any swivel/pivot bench, be aware of this potential hazard. Once you see the results, it paints a strong picture in your memory. Personally, I do not lean back when shooting, and see no need for doing so.
This is just a PSA for those considering making their shooting bench into a lounge chair. We're all free to do as we please with our own equipment, just be aware of this potential hazard. JMO JME