Hi all, I'm looking for help. I'm making a mold for the seatback of my Tesla Model S. I've sanded the surface with a 1500 grit. It's silky smooth. I put modeling clay into the crack surrounding the seatback. I'm now looking to create the flanges for the vacuum tape. This design is a little tricky for me. I tried corregated signboard but with no flat surface on the underside. I'm having trouble getting it to stick. I'm now thinking of using pour foam to get my flanges. I'd wrap the piece in a bag, find a big box to where the foam will ooze out the sides of the piece and create the flange. Suggestions?

You should be able to use hot melt glue (gun) to glue the correx on, to make flanges .. A photo showing the reverse side, close up would help advise you ...

Most pieces will not have a nice flat reverse side to attach the flanges to.  I've sometimes had to "build up" a framework from correx and wood /plywood pieces on the back of a part to support the flanges.

The "pour foam" method will most likely be very messy compared to "building up" with correx and hot-melt glue.   If you're worried about marking the reverse side you can tape up the places where you put on the glue.
 Your existing seat-back is "the Plug" in this case, and any time spent om polishing it to perfection, is saved on polishing both your mould, and the end product..

In some cases, making a good usable "plug" from an original can be very difficult, even impossible, without damaging the original... sometimes beyond repair   This has happened more than once to me on fairing parts for bikes..

"Sapere Aude"... Dare to KNOW!

The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind...

103% of all people do not understand statistics...

Do not adjust our mind, theres a fault in reality :-)

It's also easier to cut the flange into multiple pieces rather than trying to stick it on as one big piece. Coreflute and the likes are relatively flexible, but the tension it creates on the hot melt glue often causes it to pop off. So it's easier to cut it into 2 pieces rather than bend it. 

Hanaldo, you beat me to that one...    I tend to cut out a lot of smaller pieces of the Coreflute (Correx/Signboard... ) and to mix it with other materials, like PU sheet, plywood, filleting wax,  e.t.c.  I sometimes put steps and bends into the flanges, to get them to conform to the part.  It can become quite a puzzle --

I do not think I ever managed to set up a pattern-part for making a mould on just one unbroken piece of Correx ..  There's a reason the originals were made from thermoplastic mouldings or glassfibre -reinforced polyester..

(Complex shapes --- )

"Sapere Aude"... Dare to KNOW!

The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind...

103% of all people do not understand statistics...

Do not adjust our mind, theres a fault in reality :-)

Here are some more photos. https://www.dropbox.com/sh/oz3nxe5a8no7blz/AAA-3xJQZbWWgUJJ264wQq1Ta?dl=0