I just went to FedEx.com and rated from Los Angeles to New York. The only rate that came close to $16 was a FedEx medium box using one rate pricing. So I guess it depends on what you mean by "across the entire US". XL box was $31.36 using standard rate. The dimensions you listed would round to 12x11x11. All non-fedex packaging gets dim weight. FedEx packaging may or may not. That's why you can sometimes see a large variances for a similar sized box. What would happen if you select FedEx box but use your own packaging? You might get away with it or you might not. Which reminds me, I had a customer complain that when she dropped off at the location where I worked she got billed one charge. When she dropped at another location, she's got charged less and wanted to know why we were over charging her. We showed her how we rated her shipment and figured out the other location wasn't doing the dim weight and was under charging her. We told her we would correct the other location. 😁 Marking residential helps you get a more accurate rate upfront among other things. Also Express saver rates didn't disappear when I rated the FedEx boxes. More on reddit.com

Yes, assuming you have an account that allows one rate to be billed to it, or can visit a FedEx Office or FedEx ShipCenter https://www.fedex.com/en-us/shipping/one-rate.html More on reddit.com

I’m not sure how much experience you have moving. You will not have the same amount of things as you think you do. With everything spread out and unpacked in a house/apartment, you don’t mentally understand how much space it takes up. Even compressed, deconstructed and tightly packed, things take up space (and weight). I chose a Ubox because the shipping option was either going to be individual boxes/totes with a label slapped on them, or everything on a bare pallet in totes and exposed. With the Ubox, everything is protected from the elements and immediately behind lock and key you have control of. I just felt it was all going to be secure and I had more control of protecting my things this way. I suggest packing everything you think you are going to keep, even if you immediately will unpack it to use it before you move, to give you a mental and visual check to see how much you will have. I thought I had downsized to only a few boxes myself and that my Ubox would end up being half empty. I completely filled it. But it’s because I had two wire shelves I kept up to hold the smaller boxes and knickknacks. And I had forgotten to take into account the actual mass of my bed as well supplies for my pets. It sounds like you don’t plan to have that. I don’t have anything like appliances, couches/chairs or coffee tables and hutches etc. even my bed frame folds up. I had a stack of various 20, 30, and 40 gallon totes that ended up being twelve total and 5 gallon totes for books that ended up being six total. I would say the totes took up about half of the volume of the Ubox to give you a mental visual. Measurements also helped, I actually took some painters tape, and marked out a corner of a room the measurements for the Ubox to do a trial of packing my totes, to see if everything would fit before I ordered it. More on reddit.com

10KG and 25KG boxes are flat rate boxes for international use only. They can only be used for International Priority service. The FedEx Small/Medium/Large/XL boxes can be used for International Priority or Economy but they can't be used for flat rate shipping when shipping internationally. More on reddit.com