I don't use ROR sitemaps anymore. They were good at the time they were emerged, gradually they got dumped as there was no such benefit. In fact, ;people complained that they got into issues with crawling using them.
I would say that just use the standard format ;XML sitemaps. ;
Just my 2 cents.
W.E. Jonk: From the expert panel in this weeks SEO Questions hangout on air on 01:19:32 into the YouTube video: