I got a 4x8 sheet of my favorite MDF at Home Depot. Out of this sheet, I was able to cut a piece big enough for the front longeron template, and all of my bulkhead form blocks. I cut it outside with a circular saw, and that dust STILL got all over everything in the shop. Wear a mask!
Bulkhead blanks
The aft bulkhead plotted for cutting on the band saw