Not sure if I've done anything wrong, but I have granted the default and admin groups "nodecay" permission and the boombox is still decaying. I tried crafting a brand new one, still decayed. Reloaded plugin, crafted a new one, still decayed. Have I overlooked something?

Sounds like you did it right. After granting perms, they should apply to any new boomboxes placed, and to all existing boomboxes if you reload the plugin.

I will test this again after work to make sure. Please DM your Discord username so that I can screen share debug with you if I can't reproduce the issue.

Merged post

Turns out this was because you were using the portable boomboxes, which this plugin does not affect. I've updated the documentation to clarify this, and to suggest using the Never Wear plugin for those, simply by adding the fun.boomboxportable item to its config.