A 5 gallon bucket with one of those spinning upholstered tops is what we found very workable.
I have also used a stand up model, ambidextrous coupled with a Hoppe's swivel gun holder. Very nice, spotting with the gun scope instead of binoculars. Use larger diameter tubing because of the longer legs.
We used pipe flanges on a hardwood block sawed at an angle. Your brackets are a step forward.
FWIW, you can get IMC electrical tubing which is threaded, and much lighter than rigid iron pipe. My next bench project will use it.
