If you are damaging the casing threads of the tire inside and nothing is puncturing the tire, then I'd have to think you are running too low a pressure for the things you encounter while riding. If you can't avoid those things, then you need to increase the tire pressure some regardless of what the calculators tell you is your ideal tire pressure.

For every flat tire you get, you have to identify what caused the flat.

Do you remove the tube and lay it on the tire and rim, all in the same orientation they were when the tube was inside and find out where the hole in the tube is compared to what you think flatted it?

I use to run Kenda's on my bike with 27" wheels. While they weren't the best of tires since I bought the cheaper Kenda's, they didn't seem to attract flats.