I would say this, I do side with Sodo and Schattenu on this - you have my support. You seem excited and eager to see if this can work. As Tony Stark said in Iron man, " Jarvis... sometimes you gotta run before you can walk". Hence I rather not get in the way of something that could potentially be another successful real life encounter.
Apologise for all the confusion eariler on CONCAVETUMMYLOVER. I was attempting to put myself in your shoes in this situation. And to be perfectly honest, I am not as bold and daring as to have my contact details associated with something like this. Talking about your fetish to your mates is one thing but sharing it with the world - I would need someone to hold my hand and for them to offer me a lollypop to go through that ordeal.
Hence I was attempting to suggest, instead of taking a 'direct approach' to meeting someone who shares your interests, perhaps trying something 'indirectly' might serve to your advantage. My concern is that being too blunt as to what you want might end up creeping the opposite sex away.
Thus I thought, rather than listing your "wants" bluntly within an advert, you might try wording it as such as to 'kill two birds with one stone'. The following I think, does just that. If there are any women with your interests, they'll surely contact you. At least if all else fails, you can expect someone reading this craigs to perhaps devise you a better one!
This is my take on how the ad should look:
"I'd like someone to help me to come up with an advert to put on the 'casual encounters' section of my local craigs list. An ad seeking a female partner who'll help me fufill my tummy/navel fetish fantasies.
I'd like her to have a slim tummy, flat and toned. I'm not talking six packs or anything, but a sexy shapley waist with a supple softness."
Of course I would condense it as much as possible!
Credits, T&N.