I am with Sound Guy. I am also glad to hear that you read the posts regularly. You asked a very good question and you got a very good answer. Sidewall indentations are not to worry about, they are actually stronger than the rest of the sidewall.
If you read the posts you will learn that tires need to be taken care of and regularly inspected. 5 years is a good rule of thumb for replacement times. I know you are aware of all the issues that might move this date back or up. You are already paying attention to your tires, good for you. Enjoy the trailer.