To keep the cost down I would use $11.25 Goldwood 7 inch poly woofers(fs=35), and use four of them per side in a sealed design, to keep the bass tight. Modeling on WIN ISd, I would need a 1.5 cu ft box for each. To save on weight, I would use 12 inch sonotubes with 3/4 inch MDF end plugs, and lots of fiberglas fill.

Crossover would be at about 200hz. The modeling shows it ruler flat to 40hz, down 4 db at 30hz and down 7 at 25 , which would have to be equalized out(system already has active crossovers and a DOD constant Q equalizer.)

What do you think?

What's neat about your idea is that the cones are already silver.

Just something for future thought - leave some room for future expansion. I just think 8 per side will provide the bass you need.

I just finished the 8 - 7" Dayton Aluminums test boxes (sealed) and they sound great. Today or tomorrow I'm going to start on the other side (channel).

I'm still going to do the Goldwood Silver Poly's - 8 per side in the future. Don't know about the Dayton 8's Bitty-Booms???
I might turn the Dayton 8's into a full range line array (8 per side ) with the Hi-Vi B1S 1" Mid/Tweets #297-411. Sometime next week I'm going to test the Hi-Vi's with all of the woofers I have. To see which will match the best.
Good Luck!!! Rudy