I also accessed the blend doors from the frunk when I did this repair as that seemed to be far less invasive that cutting the ductwork behind the head unit. It is possible to recover both blend doors this way although I'll readily admit that getting to the inner door was a PITA. I covered the doors with craft store self-adhesive EVA foam sheets. This has worked well for me.
You can see how I did it here -
https://rx19jones.wixsite.com/projectboxster/projectboxster7