Well, guess I will be doing this one over the next couple of weeks. Figured out the fuel as I already have a 60"x24" hitch mounted cargo carrier that I use for overlanding/camping. A couple of 2gl RotopaXes will mount nicely laying flat in that carrier and still allow me to fill up the soft sided cargo bag that I use to keep everything together for camping. Not planning on camping this one (North Rim winter? Meh.), but I'm looking longer term. The extra capacity now only costs about $200 which is a bit more palatable for a small increase in capability.
From I-15 just south of Saint George, the NPS has the distance as 85 miles to Toroweap Overlook. And the distance from Mount Trumball SH to Whitmore Overlook is right at 20 miles one way, so easily doable. From the trip report over on Expedition Portal, they were able to bet gas at the Bar 10... Shouldn't need it, but it is worth a phone call out to them.
What else? The question is if the NPS has Toroweap blocked off (more traveled than Whitmore)? The North Rim is supposedly closed over the winter, but what does closed entail (the visitor center and campgrounds or do they go Byzantine on your ass if they come across you?)
So, if anyone is interested, I might be posting this one up as a rather long day trip in the near future. Depends on the info I find over the coming weeks.
Red line / track below is coming in from Saint George and the map layer is the NPS Visitor from CalTopo (you can find all this on Gaia online).