I have a 4 inch cross tube on the FEL. Carry just about anything. Chain - shovel - plastic pipe - etc. Have two six inch chunks of plastic pipe that are capped. Shoved in each end will keep anything inside weathertight.
Lots of miscellaneous carrying options with the toolbox. I also made some tool racks that u-bolt to the ROPS for long tools. I try to not load really heavy items into the tool box due to working on hills constantly (high center of gravity), so still thinking about chain storage options.
I installed a grill guard and chain bucket combination. I carry a 20’ chain in the bucket below the grill guard. I also installed a steel toolbox on my ROPS cross brace where the useless plastic box was. I carry a 10’ chain in there.
For my use, it is the shorter chains that get the most use. I have at least four six foot lengths with a slip hook and a grab hook fitted to alternate ends.
If I expect to need a chain, I just drape one or more between the three grab hooks welded to the top rail of the bucket.
It does get cumbersome with the 16 foot chains however.
John Deere 3033R, 855 MFWD, 757 ZTrak; IH Cub Cadet 123
As noted previously, a ballast box is a great place to carry chains, you usually need some extra weight there anyway. Here, you can see I have two 10-footers laying on top of the concrete in my box. I left the concrete about 2 inches shy of the top of the box, so I could use that space for carrying chains, hooks, and other tools:
On other occasions, such as when I'm not running a ballast box but still need a chain, I hang them from the front brush guard. You just have to be careful they're hooked securely and not dangling to the ground, since you don't want a chain getting under a tire and tearing off your brush guard.