Spent the evening wrestling with layout on a 18w x 13.5 deep top plate. The box is 5" thick and in some places I am running short of room. Three L-C filters, two for the filaments, and the main HV give this thing a mass like a respectable power amp. I am losing a half inch at each edge, so the realestate is a bit smaller.

If you guys go for the top plate and wood base construction, getting a haldle on it to pick it up is sometimes a PIA. Take a 1" holesaw and at the lower edge make four overlapping holes so you can stick your fingers in. Make the edges a bit rounded, and it is a great sol'n to the trouble of sticking handles somewhere.
regards,
Douglas