I am just completing my bimini for my B331. I made a mock up frame using duct tape and light lumber. Once I determined the dimensions I had the stainless tubes bent and ordered fittings. I positioned the mid support just ahead of the double backstays. Once the steel was ready I fitted it on the boat and again used duct tape to simulate the canvas and location of back stay openings.I then delivered the assembled frame to the canvas shop. I expect to install the unit this weekend.
I am in Canada so prices may be a bit different - I paid 560.00 Can (360.00 US) for all of the metal items and 300.00 Can. ( 195.00 US) for the canvas. If you are located in Ontario I can pass along names.