recently had a large ish sully shipped in as a rescue around roughly 38lbs or so came in a thick black plastic tub BUT they used wood from pallets inside to make a frame on the bottom top and sides. this prevents collapse. the issue is it added a lot of weight but they were allowed to ship them. was through fedex. i wish i thought to take pics of the packaging. the person who packed them like that said they did request he open in so they could see it and then re zip tied the lid back down about every 2-3" around the top.
And yesss….the answer was try another location with different people. This other FedEx was just excited about a tortoise being there. Easy and crossed the country in 15 hours.