No. Just no.
I was hopeful that I could leverage Let's Encrypt's automation to alleviate the issues that consistently shrinking cert lifetimes bring. After working on this for a day or so, I realized that you are requiring that sites allow unauthenticated traffic via an unencrypted channel to a folder on their webservers.
It amazes me that I have to point out what a terrible idea this is. The insistence that "the internet" means "anywhere" is a logical fallacy. Restricting access to those who need it is Security 101.
Good luck, I guess. Maybe enterprise adoption isn't important to the organization.