If you have a chance, read the selection of HST letters that are published. I've read the first two volumes and can't wait to get my hands on the third one https://www.thriftbooks.com/series/the-fear-and-loathing-let...
He was a very prolific letter writer and kept carbon copies of almost everything he sent. This is the one he sent to Anthony Burgess when he was editor of Rolling Stone: https://www.openculture.com/2016/05/hunter-s-thompson-writes...