Because the GrevePipe I'm planning on using is so long, I had to make a modification to the underside of the body at the end of the pipe.
It almost made me cry to have to cut-up this airplane but Ijust followed the instructions from Ole Fremming excellent web site and all went well.
Make a balsa plug, cover it with film and shape some class cloth over the top.
The finished quality of the surface that was against the film is quite remarkable. Very smooth.