I think the OP has made his choice, but I just want to add my opinion. First, I hope it's not legal to dump gray water on the ground in any state - it's not water, but wastewater, and has plenty of chemicals, colorants, and pH inconsistencies.
My wife and I can go 4 days with a 40 gal black tank, and 2 - 40 gal gray tanks. That's with cooking all meals with the necessary cleanup, along with satisfactory, quick baths and showers. I have the smallest tote, and use it maybe once in a couple of years. I always carry it and it fits in a small space. I can see plenty of advantage of having pneumatic tires, but my compromise suits me fine. I can lift it onto my truck, or tie it to the hitch for a longer distance.
2011 Sabre Silhouette 260BHS
2006 F-250 6.OL