I believe that you can consider in your particular object's case the "Scaling Rail" as a third rail!

Ps You have also the middle section overlapped! ;)

else Network works like a charm : Yo have just to close the extremities by a plane if wanted!

Hi Pilou,
is the solution shown by you the network-solution?

Yes ;) was writed "else Network works like a charm"
but i have killed first all overlapped curves! (middle section, side edge...)