Did you ever check if the tent itself is trapping heat, since a breathable cover only helps if air can move around it? I'd crack the tent door open a bit on hot days and skip the cover completely until you get a multi-layer one.

One thing that's not quite right here... you say you never answered that call, like that's the whole problem. But the call wasn't the moment it went wrong, the three years after were. He left that voicemail and then you spent three years telling people he was greedy, and that's the part he'll have a harder time with. So when you do reach out, don't lead with the voicemail like it's a magic fix. Lead with the fact that you bad mouthed him to everyone for years and you know that was wrong. That letter in your drawer is probably fine, you just have to mail it knowing it might take him a while to come around, and that's fair. Pick up the phone after you send it, not instead of.