A couple of years ago, Larry the Black Baron and I were talking about the old hollow log Gee Bee R1 Walt had kitted way back when.
Inasmuch as it required a large block of balsa, then much more routing out (for the massive fuse diameter) then the cowl, wheel pants, wing mounted gear...it wasn't worth doing from a production standpoint. 
Larry was also reticent about the prop diameter and that massive cowl. He suggested I do a 'prototype', and gave me the specs for some plunge routers.(end mills) When I asked about an old Musciano plan, Larry said he'd never seen one, nor the R1 box. 

I drew up some plans, (actually referred to the old 1/2A Cleveland plan, reducing its size to Musciano parameters) and bought a balsa block. (probably in the 8 lb. neighborhood)
It was evident I was in for some serious 'hollowing'! The fuse had to be split, as it tapers severely from just aft of the leading edge...
The project got shelved, as I was just finishing my shop...

Today, I read Steve's post about the Hollow Log foam project, so I went and got two green foam blocks from the Dollar Store.
Each measures 2-7/16" X 2-15/16" X 8". One will just make a Gee Bee fuse...Let me carve away what doesn't look like a Gee Bee, then wrestle with some pics. I plan on using a solid balsa wing, as the gear mounts to it. Cox Black Widow, from our old  Mouse Racer...

Steve, there was a box of this (floral foam) in blocks; $1 apiece, these blocks are sealed in clear plastic. Very dense, but my take on foam is that it's not too 'stiff' in a monocoque structure!

So, I'll split the block down the middle, and glue the shaped bottom and top onto a horizontal basswood crutch. Some hollowing for bellcrank and pushrod, maybe a remote tank rather than the Cox attached. But with the crutch, I could go either way...

Man, this stuff's LIGHT! 

Anyone tell me where I van get one of those neat digital gram scales???

Horrible Fate (Harbor Freight) has them for under $15. I have three, one in the car for trips to the hobby shop, one in my office and one in the workshop.

  If you are substituting the foam for balsa block, consider a layer or two tissue paper and Elmer's glue over the finished surface. Once it is built up enough, you can dope it. Might even be able to hollow it out some.
   Good luck, have fun and keep us posted,
   Dan McEntee

Steve, John and all:

Steve's right, this stuff's crumbly! Tried my big band saw, hand jig saw, 60 grit sandpaper...Phooey! LOL

Home Depot did NOT have the blue foam, I need something real dense. (like the old ACE wing halves...That was dense foam)
Going to Lowe's big box store. Maybe the craft stores have some dense stuff.

Mike, sorry to hear that it didn't work out with the floral foam. As light as the stuff is it would have been great to see a way to utilize it.

you can scavenge some dense foam from shipping boxes for large items. Sometimes they use the "Elapor" style of closed cell foam like the Multi-Plex arf R/C planes are made out of. Best But / appliance / electronics stores may let you look through the re-cycle box area - especially if you tend to spend money there.