The third tip is the heat gun!
The next two pics show my seats fully assembled with the new upholstery stretched as best as I could do by hand. Some wrinkles.
I installed the seats and heat gunned the seats in the car but I guess they could also be done outside. The heat gun is set on HIGH. You must get things really hot to properly shrink leather. This is like doing window tint but if you melt the tint you waste $20 of tint, If you burn the leather you lose $600! I would be very careful doing this on vinyl so be aware!
Here are the Porsche Seats after heat gunning.
And a section closeup:
Before heat gun:
After heat gun, It won’t remove big tucks but all the smaller creases will come out. Rather amazing actually.
You work with the gun 1-2 inches off the leather using a circling movement. I also used a wet sponge to dampen the leather first. It gets smoking hot - well almost but you can see it shrink. Do a bit. Work another area, then go back. Small areas. Easier than shrinking window tint as the leather shrinks in all directions and no squeegee required.
Overall project took six partial days. At my age day one was remove the seats. Days 2, 3, 4, 5, I did one cushion per day. Maybe 2-3 hours per cushion. Day six, I put them back in the car and heat gunned.
In reality, this could be done in a long weekend but get ready for tired sore hands from pulling leather.