While the mast is down I'd like to put on an innertube mast boot. I tried a leaky tractor tube that I had on hand. It seemed a likely candidate when I draped it deflated over the mast, but it ended up being too big. I'm wondering if anyone knows what size tube has worked well for them? The mast circumference on my 38 is listed as 21 and 7/8 inches. I can't find anywhere that lists girth of a deflated tube. I'd like to avoid buying and cutting up a bunch of tubes to find the right fit.