Hey Leyland,... well,.. first,.. very kewl shape!..... make this less of a problem (since this is a mirror/mirror) and focus on only 1/4 of the bottle.. and offset/trim the surfaces or whatever new geometry there to create your 1/4 core.. (then do you mirror/mirror)
Thank you very much, unforgettably with cool shapes come difficult challenges.
I have given it a go, but no cigar.
If you have time would you be able to have a quick go please? I'd appreciate all the help I can get.