John,
They make several different sized angle supports that you can use to support the wheels from and they can slide along the strut channels to engage the vessel wall where needed. They also make 45-degree angle connectors so you can cut the strut channel with 45-degree miter ends and join the segments together to make an octagonal shaped steady rest which will provide closer engagement from the channel to the vessel wall all the way around the piece. I used the heavy gauge strut system which is also available in a half size 3/4-inch by 1-5/8 wide channel and some of the channels are made with a 14-gauge metal offering in various materials like painted steel, aluminum, stainless steel, fiberglass and anodized steel. You could easily cut the pieces and weld them together to eliminate the mechanical joints and still be able to use the modular fasteners and brackets that fit the channel. These strut channel systems are manufactured under different names, Uni-Strut, Power-Strut, Super-Strut and Kindorf etc.