I think the winnigas.com site is a good one, as it's winni specific.
But I thought I'd let everyone know that gasbuddy got back to me to thank me for the idea to have an option to cover boats. So keep an eye on an update in the future!
In the mean time, I'll try gasbuddy and/or winnigas.com, both which make it easy to report prices live while you're on board and are currently loaded into my smartphone.