Builders Trestle - doesn’t just looking at this full your mind with possibilities?
On Amazon, £40, weighs 12kg, can take 400kg, built for heavy duty use. Height adjustable available in 3 sizes. I bought one for a construction project but every time I look at it my mind wanders. A lot of people post here about modding IKEA stuff which is built down to a price. This costs less than a lot of IKEA and so much better. You could buy multiple and use for so much.
The first mod I was thinking was a separate footing wider diameter hollow pipe and cutting off the keg so that it would go inside. That way could be stored flat.
The top bar is rounded so feels comfortable but could so easily attach wood to give better base for sub to be bent over. They could also be stood in front or bent over and tied to it. So many fixing points available.