Though either way will work, putting the ring on the inside allows the nut plate rivet buck tails to be against the thicker ring material. It also means you'll have one less external seam to possibly leak.
F1 Rocket and F4 Raider components
RV and Rocket Accessories, Tailwheels, Tools, & More
F4 Raider - under construction
F1-H Rocket "Crazy Horse" - sold
RV-4 "Chief Pontiac" - sold