You know, I have an ileo and my first stoma lay right along an older surgery scar. The wafers never laid right and I had to "fill in" with paste - but that never worked great for me. Convex flanges helped, but it wasn't until 2002 when I had to get my ileo revised and the stoma moved to the other side that the products (Hollister) worked really well for me.
I don't use paste anymore - it seems to compromise the seal, and is a gigantic pain to get off the skin when I change my stuff every 5 - 7 days. One thing that really helped was to make sure and get the smallest appliance possible for my stoma, and cut the hole almost the same size (after this long, I can eyeball it and get it right every time).
Another thing that helps me: when I change flanges, I peel off the old one, wipe everything down till it's clean skin with a warm, wet paper towel, swab it off one more time with a wet paper towel, then dry the skin thoroughly with more paper towels. NO SOAP!!!! Paper towels (or paper napkins in a pinch, snitched from a hotel restaurant, ha ha) work MUCH better than any fabric I've used.
I can do the whole operation, from cutting the flange hole to clipping up the bottom of the bag, inside of 10 minutes now, as long as my guts are not putting out a bunch of stuff during the process. I rarely have skin issues anymore, unless I get lazy and leave it a day or two too long (you will know, your skin will itch and burn).
Good luck! Everyone has their own issues, and their own solutions. Hopefully some of mine are helpful!