Hello again. I forgot! Welcome to the forum.
It will help if you update your profile and let us know what kind of trailer you have. I found some good information in this thread. Especially post #11 scamp 4 lug spare tire mount pic?
There are plenty of topics to be found using the search feature. Though I still couldn't find how most through shell tire mounts are weather sealed. Perhaps they were all glassed over as I read in one instance. Mine is an older model and does not have the plywood backing plate listed in the thread above. The bolts are all loose.
I have purchased some extra nuts and rubber washers. The nuts to prevent the tire from being compressed directly against the fiberglass. I read in one post this wasn't good but I wonder if it's better than having the tire just hanging from three bolts. No rear bumper on my trailer so no extra support there. I will also look for someone to make plate with the bolts attached that I can mount it on the inside for extra weight
distribution. I saw that pictured here but couldn't find the thread.
edit: extra threads
Spare Tire Mount: Play or Normal?
Spare Tire Mount on Boler 13ft