I'm sure he's talking about building the seat from scratch, and the upholstery chapters in the scratch built hot rod e-book won't help him with that. There's a lot more information in the interior section of this forum about making panels and seats than is in the e-book, all he has to do is do a search.
There's a reason why you don't use drywall compound and Masonite for panels in a car interior. The reason is there are better, easier, less expensive, and less time consuming ways to do things. That's why people who do upholstery for a living don't do it that way.
Here is a thread about a scratch built t-bucket seat: CLICK HERE