After considering other shapes I decided to cut a circle to lay in the bottom (actually, it would go up the sides as well). I grabbed my compass and opened it as far as it would go......4 3/8" radius which would give me an 8 3/4" diamater pad. Comparing to the size of the double gourd (which is the shape of a Big Bo gourd) it looked about the right size. I traced out the circle on the 1/8" thick cork. If you put just a little pressure and scratched back and forth, you could almost cut through the cork with the sharp edge of the thick pencil lead. Cutting out the circle with an Exacto knife was easy after marking it.
I sprayed 3M Super 77 Spray Adhesive on the cork....and waited 30 - 45 seconds for it too get tacky. I rolled the cork and slid it thru the access port. I slid it around tryind to center it. It was difficult to tell when the disk was centered. Finally got it in but it was difficult. Didn't look to bad though. Surely a better way.
On the next one, I decided to drill a 1/2" hole in the middle of the cork disc and I cut the radius on one side with my exacto knife (one slice from the center straight to the outer edge). I sprayed it and after the adhesive was tacky, I formed a cone by overlapping the disk where I had sliced it (see pic) . The tacky adhesive held it in this shape.
I rolled the cone and slid it thru the access port inside another gourd. This time I placed my finger in the center of the cone (in the hole) and shifted the cone around till I could feel the drain hole in the center of the goud. Instead of centering the cork disk, I decided to offset the cork 1/4" or so to the rear (this is where the nest is built and this made the cork end just at the entrance of the gourd). I pressed the cork against the gourd and worked it from the center to the outer edge of the disk, and, I worked it from one edge of the slice around to the other edge. In the end, the cork overlaps about 1/2" -3/4" at the outside edge. This was so simple I ended up doing 8 double gourds and 6 Big Bo gourds the same way. When the adhesive has cured, I will drill a few drainage holes thru the cork and plastic gourd.
Be interesting to see how the cork holds up. The martins will now have a cork lined entrance tunnel and a cork floor in the nest area of the gourd (no tunnel on the double gourds). Here are a couple of pics of the interior of 2 different Big Bo gourds:
