Just wrote a post only to lose it GRRRR!! So, in summary,
Re: Towel Rails
Go for normal size rails where they fit and then put a robe hook (at towel rail height) next to the shower doors.
Like this: (these are cool because they fold away when your not using them)
http://www.ikea.com/au/en/catalog/products/10161219/
or keeping with the bum theme of your thread:
http://www.ikea.com/au/en/catalog/products/10198430/