Where I worked I used Rhinoceros 5 and I remember that there was the possibility of defining the continuities for the network of curves ... although I must tell you that a friend of mine modeled directly using a single surface and then mirrored it .... I don't remember which program was honestly but i know it modeled in nurbs ... i should ask.
I asked Michael for support who was very kind in following me in the modeling phases ..... at this point, since as it seems it is not easy to model it, I will try a different modeling approach .... for now I had to buy various programs for photo editing and I can not "afford" Rhinoceros .... so I'll try with Moi inventing something :)