I got my paniers to D*C from New Zealand with the help of a friend but I essentially used sports tape to temporarily hold the ends of the bones in place.
I leave an opening in the tape and have a nice 10" overlap wherever the shape allows for a slightly flatter line. In paniers it's at the back, for any hoops that's potentially the front- unless the skirt is heavier in the back and it'll be a bonus little extra support.
I tape the ends of the bones and then pull the ends out, evenly on each side and gather the fabric over the remaining boning. The ends naturally fall in shape and the paniers conertina flat. I think I have a photo, if not I can get some.
Basically the paniers fit flat inside carry on luggage sized suitcases
My short bustle fits inside a hat box, so it is very doable
If you use hoop wire and have it welded closed I'm not sure there is much you can do.
To help, you can also make a support of densely layered firm net, basically a classic tutu (not romantic, though that can help as well) to help give a little lift and life if there is not much time between unpacking and wearing. The net can be hung upside down over night and will pack down flat with anything weighty sitting on top. I have a bustle shape net petticoat made up of more than 30 yards of net that packs down to the size of a pillow, then, spring! And it can be laid flat with the weight of other costume elements to flatten it in transit.