The dev kit for the XBee Cellular comes with the module, XBIB dev board, and a couple antennas and cables. I wanted a simple case the dev board and antennas could sit in to make it easier to transport and avoid the antennas just sitting free on my desk.

I'm sure the close proximity of the antennas is not optimal from an RF perspective but I did not notice signal degradation compared to them just sitting freely. I tested it specifically with an XBee Cellular Verizon LTE Cat 1 dev kit I had (XKC-V1T-U, https://www.digikey.com/short/jm2npj), but any kit using the same revision of the XBIB dev board and antennas should work fine.

There are holes in the case that line up with the holes in the antennas so you can insert a small bolt and nut to hold them in place if desired. As long as you're not turning it upside down the antennas will stay in place fine without bolts.