Hi Judy...
Just reading this thread... I'm a chubby girl, too. My stoma is new. I had surgery just a couple of months ago. So getting used to my stoma is a trial and error thing for me.
I use ConvaTec as well. They have a two-piece pouch system with a moldable flange/wafer. My stoma is not that big. Maybe 7/8 of an inch. It also doesn't stick that far above my skin that well either. Maybe an 1/8th of an inch or so, but it's almost flush with the skin on the belly button side. I do use Eakin rings as well. I haven't had a leak in about a month and a half and wear my appliance for a week. I change on Sundays.
I make sure my skin is DRY after I shower. I pat with a towel. I don't rub though. I use my hairdryer. I put a layer of skin barrier on (little packets, but I can't remember the name. My surgeon gave me some mastisol samples but I've not used them yet) and I blow dry again until dry and tacky. I put my ring on and I flatten the outer edges of my ring against my skin before applying the wafer. I mold my flange (they make these in convex, too) and put my wafer on and then I use the blow dryer again (on a medium setting) to get some heat there and I firmly hold that against my skin for a good two minutes. Then I put my pouch on, like Tupperware. I can audibly hear it snap together, so I know it's tight.
The one thing that I feel has helped the most is I wear a belt with my pouching system. It just helps hold the wafer tighter against my stoma to prevent leakage. I rinse my pouch out at least once to three times a day and I know that if I didn't wear a belt, it would all run under the wafer and under the ring. I think those rings are the best thing ever invented.
I've experimented with a few different pouching system brands like Hollister and ConvaTec and NuHope and I still like ConvaTec the best, but I did find that one of the brands I tried had a horrible reaction with my skin. It was awful. It left blisters under the wafer. But... I've also heard that if you use Milk of Magnesia on irritated peristomal skin and let that dry before applying a new wafer, it will help, too.