How to prevent chub rub from ruining pants? Sewing Machines Parts and Sales in Los Angeles

Hey there! My SO has a pair of canvas pants he loves and would like for me to replicate, with some minor changes. The only thing I’m trying to figure out is how to reinforce the inner thigh/crotch area. My SO has big legs and that seems to be the part of pants that wears out first. He doesn’t wear pants too tight, or too loose, he just has larger thighs.

I’ve used the Google, but to no avail. There’s lots on how to repair them, but not how to prevent it from happening.

Thank you in advance for your help!