The Blocks for attaching fabric to around the Tank Filler Neck were made of of a soft wood 1/2" thick with a cross grained ply of 1/16" veneer of mahogany on the top and bottom, making a thick 3 ply plywood. The veneer was badly broken so I replaced it with 1/8" plywood. There is plenty of room for up to 3/4" thickness. Double click on the pictures and you can see the dimensions for the hole, etc. I epoxy varnished the blocks which should now last for the life of the plane. You could probably make them from 3/4" plywood if there is room to widen the thin section a little. On the left wing the filler is that close to the root rib. I could not get the right tank that close. 
They're stuck in place with black tar like roof sealant. Once everything is painted I'll seal the gap better with RTV to keep water and gas out of the wing.
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The tank had some spots where fuel had stained it and while there was no evidence of a crack or wear I pressure tested the tank to make sure. A coupler for my 2" hose on the shop vacuum fit snugly over the filler neck. My shop vacuum has a blower connection as well as vacuum. The blower side puts out a nice 2 psi. Isn't it great how life just works out some times. I taped over the gauge opening, it leaked a little, and plugged the drain. .
I connected a low pressure gauge to the fuel line to monitor pressure and used soap solution to look for bubbles on the stained areas. As expected there were no leaks. The stains are in areas which seamed to be the natural flow paths from spillage around the filler neck, still worth checking.
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The wing is now in the tent ready to install the fabric. All ADs and service letters are complied with, the tinnerman nuts are all on, wire is run to the nav light, and the tank is snugly mounted on it's padded ribs. The wing rib lacing is done and all areas needing chafing protection are taped. After a very busy summer working and traveling to fly-ins during dry weather it is now raining here. Once it dries out again we'll get the fabric on and work to get both wings through color before winter.
