Here is the enclosure I made. SO3: XXL Mega-Enclosure and Dust Collection
I am a bit puzzled how and enclosure will work for 8’ long material unless you have doors on front and back. I had planned to do a video showing the features of my enclosure, but have not gotten to it yet.
Your main question was height, I am happy with the 26" overall height, but could have gone lower due to the small diameter ( 2") hose- the larger diam you use, the more height is needed. Sending the hose out the back works well. And pls note , I mounted the control box OUTSIDE the enclosure. Cleaner design and work environment & easy access.
As a summary:
Th unit sits on a frame with a Torsion box top.
The TORSION box was made from 3/4" bottom and sides,
1/4" top and
1/2" internal eggcrate/half lapped cross members every 8" in both directions.
The enclosure is pictured here finished. I am very pleased with the result . The router noise is very minimal. The 63 dB Nilfisk vacuum is a lot louder than any noise emitted from the router when cutting. I found a low cost variable speed control for that which lowers the vacuum noise considerably. I used mass loaded vinyl on the interior of the box 1/16" thk to contain the sound, and 2 LED strips ( 30 K color) on the interior.