Wing, tailplane and fuselage are better treated while separated, except for the final decorative finishing.
Sanding is done between all stages.
First all the naked wood gets a coating of thinned cellulose dope.
Then all surfaces should be covered with 1 oz glass cloth (the lightest in the hobby shop) and epoxy. There are lots of ways to do this. Use low viscosity slow curing epoxy, further thinned in methanol. High viscosity slow curing epoxy can also be used if sufficiently thinned. This is even preferred for the fuselage, since it prevents the glass cloth to rise in curved places.
On the wing it's best to use two separate pieces of cloth that overlap ~ 1" in at the root and are wrapped over the leading edge. There should be ~ 1" excess at the tips and trailing edges.
Use a medium hard brush to wipe out the epoxy over the glass cloth. Use no more epoxy than for the weave to stay visible, except for all edges, that should have an excess. Leave to cure for at least 72 hours before sanding. (At room temperature.) (Fresher epoxy dust is allergenic.)
A neat method for curing the wing and tailplane is pressing, but just hanging to cure also works. Heat up to 50 deg C (120 deg F) could be applied to accelerate curing. The time is roughly halved for every 10 deg C (18 deg F).
For pressing, after an hour, to allow most of the methanol to evaporate, the wing is put between thick (.25 mm, .01") polyethene film sheet (teflon if you can afford or get hold of it). All air bubbles are pressed out manually, and then the assembly is put between two 3" polyether foam sheet, in turn between two thick flat wood panels. The whole thing is clamped together to ~ 1" separation. Press for 24 hours. The film doesn't stick to the epoxy, and is removed easily afterwards. Pressing gives a lighter result, as the cloth gets closer to the wood. Be prepared to waste a wing in the learning process, though.
Whether pressing or not, there are lots of air pits in the weave that have to be filled. After removing all glass flash and sanding to evenness and to open the pits, a second epoxy covering is necessary. This is wiped out with a rubber slate, so that it gets into all pits. Pressing a second time is a possibility. Repeat until the surface is free of pits. Tedious work here.
The fuselage needs an extra glass cloth layer in the nose. After putting wing and tailplane in place in the fuselage, the joints are reinforced by two - three layers of cloth.
Finally finish in a color of your taste, or let it stay clear if you have done your wood work prone to inspection. The epoxy in the previous stages can be dyed. This can form the final semi-transparent finish, but be prepared that getting an even saturation is difficult.
Most enamels are diesel fuel resistant. Car paint in an aerosol can is a simple solution, and is quite hard, but two-component polyurethane enamel makes a superhard finish. If you spray paint it, watch your lungs by wearing a protective mask.
Göran Olsson, 1997 SWE-1362