Well here is my idea for foam and glass skins,...

First you would need  your fuselage built up without skins (see my fuselage page). 
 Grab a sheet of Last-A-Foam and hold it up against the side (or bottom if you are 
making the bottom) of your fuselage.  Trace with a marker all around the outside of
 your fuselage.  Lay the foam sheet on a flat surface with the marker side up and 
trim around the drawing,  trim it so that the foam skin will be 1/2 inch larger than 
the outline.  The skin will need to be made from 2 pieces as the foam only comes in 8 
foot lengths.  This is no problem though as we will build a joggle where the two pieces 
mate for a 2 inch wide glass tape.  With the foam laying on a flat surface apply two 
layers of 6 oz bid.  Apply the bid so the first layer is at a 45 degree angle to the
 fuselage, this will require cutting ther glass on the bias and will require two or 
three areas where you will butt the glass up next to each other (do not overlap the 
glass this will cause bumps in the finished product). Apply the next layer with the 
fibers on a 45 but so that the butt edges are in the opposite direction as the first
 layer.  Wetout peelply on top of the last layer of glass.  Let cure.  (these two 
layers of 6 oz make up the outside skin) 

Note: Where the two pieces of foam will butt up against each other you will want to 
sand a nice joggle into the foam before glassing.  You can make a joggle 1/16 inch 
deep and about 1.5 inches wide (fore and aft).  This will give you a 3 inch wide 1/16 
inch deep area to apply 2 two inch wide tapes to join the 2 pieces that will make up 
the complete fuselage skin. When you sand this joggle into the foam you do not want 
to go the full length top to bottom, leave the foam level with the rest of the skin 
near the top and bottom.  This foam will be removed in the future and the skin will
 bond to the longeron.  Your 2 inch wide bid tape will only join the two skins in an 
area that starts about 3/4 inch from the top to  3/4 of an inch from the bottom.

After cure hold the skin up next to the fuselage again and now trace around all the
 vertical members as well as the longerons.  Now lay the skin on a flat surface again
 and using a x-acto knife cut into the foam along each line (actually about 1/4 inch 
to the outside of each line,  outside meaning the side away from the spruce member), 
 you will want to cut through the foam and down to the outer skin but not through the
 skin.  Next use a scraper to chisel up all the foam between the knife cuts.   
The idea is to remove all the foam where it will contact the wood structure plus
 some. This means the foam should be removed all along the top and bottom edges 
as well as where the vertical members are located.  Use some 60 grit sand paper 
and round all the edges so the inside glass skin will lay over the contoured 
surface better.  Also you will want to lightly sand the area where the inside skin
 will make contact with the outside skin (glass to glass area) Now lay up your inside
 skin by applying one layer of 6 oz .  Use a paint brush and a stipple motion to help 
get the glass down into the valleys. This layer will be applied with the fibers 
running fore and aft. Use peelply in all the future bond sites (where the spruce 
structure will come in contact with the skin).

After cure peel up all the peel ply in the inside and flox into position on the
 spruce structure.  Leave the peelply on the outside skin until you are ready to
 sand and fill.  Of course you will need to remove the peelply if you are applying
 a glass tape but try to leave most of the peelply on as long as you can to protect
 the outside skin from drips. 

You may ask why all the glass to glass areas?  Well by making all the areas where
 the spruce contacts the skin you are transferring the loads to all three layers 
of glass more effectively and the glass to glass bonds add rigidity and strength 
to the skin.  The skin will be quite stiff but it should contour to the shape of 
the fuselage with no problems.


Advantages??

Should be stronger than plywood

Should be lighter than plywood (will be if vacuum bagging is used)

Should be less than half the cost of plywood.

An additional layer of glass can be added to the front area of the skin for 
strengthening up the firewall area (see below).

A joggle could be made in the outside skin up near the firewall so that 4 or 5 
layers of 6 oz bid could be used to tie the 1/4 plywood into the fuselage skins 
(8 inch wide tapes, 4 inches on the firewall and 4 inches on the skin)  This could 
be done on the sides and the bottom.

Better sound insulation.

Disadvantages

Would require more time to build

Is not proven

Remember this is only an idea and I have not tried it.  So use at your own risk! 
 You can see a jpg image at:

http://home.pacbell.net/mikemims/skin.jpg

Oh yea, you engineer types feel free to shoot this one down!  Cuz I aint no engineer!