I did something similar to the 16 foot door on my shop when I converted if from a garage. I used foil face polyisocyanurate insulation because it does not support combustion, and a shop is chock full of fire starters. Sawed it to width on a table saw, cut notches for the hinges, and glued the pieces on. I also glued some polyiso insulation to the header above the door.
The 24 X 26 shop has an estimated heat loss of 10,000 BTUH at 65 F inside and -20 F outside.