I use a cheaper frame.
I use some 20mm square timber, make it in to a rectangular frame, suitable size for my boat hull. Fix 4 uprights a, one at each corner, making sure to glue and screw these together, then use some 1 – 2 inch wide luggage strap and make a “sagging loop” between the 2 ends of the upright posts. these then easily “shape” to the contour of the boat hull without having to cut any pieces of wood to the hull profile, plus they dont mark or damage the underside of the hull or the paintwork.
if you then screw a metal eyelet at each corner, attach some rope cord to them, you now also have sme carry handles so you can carry your boat to and from the pool/car/workshop.