Here's some things I learned. Maybe it will help you.

1. I know the manual has all othose exacting dimensions... 11/16 etc. You're going to trim, sand and shape to FIT so don't get too wrapped up in the dimensions. If you cut the line fat or skinny when you stack the pieces it will be time to sand anyway. 

2. Avoid the circular saw. As light as the material is I thought it would be great. The blade will catch, jump and rip the foam. 

3. A japanese pull saw cuts like butter and fast.

4. 40 grit on the obital sander shapes nicely then follow up with 120. Use it like a paint brush to shape. 

5. The only needed true flat surface is where it glues to the underside of the seats. I went for symetrical on all other surfaces. See note # 1.

6. Check and recheck fit in the hull and height to the seats before you even think about glueing to the seats. Don't be afraid to shave an extra bit off to ensure it will fit. 

7. If there was a time for dust collection it is now. Damn stuff is like snow and gets everywhere so turn the leaf blower on yourself before you walk in the house like that or just change your clothes!

Have fun

Dean