Hi. I didn't check to see where you live to see how far you are from
Wisconsin. I am from Michigan and found Eider Flag in Wisconsin. Not sure if I spelled that correctly. They made 21 foot sections by 8 inch diameter 0.25 inch thick with an internal sleeve so that the sections could slide together. We had to choose between 7 inch diameter and 8 inch diameter. I went larger, but I had to make the Mast case and the center of the deckpod larger. It would be very difficult to do this after the fact. I think 7 inch would be big enough. There were only limited diameters available at a reasonable price. We brought them home by putting them on a boat trailer.
The sails go up and down easily. no excessive friction. We had them anodize the sections. We had connections/ears welded on by a shop. another shop gouged us making the foot. If the price is too high I would consider a hard wood foot.
We have our boat on the hard. So we plan on some work. We are planning on putting xynol cloth around the beams. Since we will have the beams out I plan to put hardwood rounded pads on the beams where the lashings are so that the pressure of the lashings is not just on the edges.
In the tall back inside corners of the mast case and the mast case of the deck pod I am going to put long hardwood wedges which in effect will be like making very large fillets in these corners.
There is a challenge involving the back beam. If you want to mount anything on it you need to put the traveler rope in front of it so that the traveler does not hit the wind vane or the wind generator, but you need to keep the traveler rope as far back as possible to be able to pull the foot of the sail tight. Inches matter here in order for the traveler to be able to keep the foot of the sail tight.