method of work pk78

[svey]

I need to sand the interior of my pk78. I would like to feather edge the tape mostly before painting the interior. How did you do it?

I've used a scraper with good result for the outside but I am having a hard time reaching with my scraper or small orbital sander.

I don't think I should try to stand on the 3/8 Oukoume plywood. I have try to stand it on edge but I'm having a hard time stabilizing it.

Yves