My 15' Radius Dish arrived today. I seriously thought making it myself but making the jig and the mess it would have created made me think twice so I decided to buy one locally (Australia)
AU $115.00 including shipping seemed like a good buy at least to me.
The following video I chose at random from a wide selection of videos on the topic to show how they are used for sanding but they also are used for gluing braces on in a go bar deck.
My search on the topic https://www.youtube.com/results?search_query=Radius+dish
Finding sand paper to fit this size isn't easy so far in Australia but I've found some in the states
I'll wait until the Aussie dollar climbs back up before buying though 0.76 US Dollar atm !!!!!!!!