Your mount may be less stable than the stock system. If there is any play between the channel iron and the trailer shell, that could create problems.
Looks like a somewhat crude fix to an earlier problem. Many report decades of no problems with the original mounting system, having the tire snug against the shell is important.
With your set up, any flex in the frame could create problems in the shell. The original design calls for a snug spare tire against the shell. The design on yours could create more stress on the shell. That vertical channel could create a lever arm, torquing against that shell.
I would remove that vertical bar, patch the fiberglass, investigate the bolt attachment on the inside of the trailer, and go back to the original design. Something could be wrong here. Very poor patch job, I kind of wonder what is under that glob of something.