1.Setting pev_nextthink on Spawn() is not reliable. Due to this, your plugin is working only if a player dropped a weapon by drop command, but fails when he is killed and game drop the weapon.
Why? Usually, when a weaponbox is created game sets the think to CWeaponBox::Kill and nextthink to gametime() + 120 in HL and to gametime() + 300 in CS. This happens AFTER spawn is called, so it overrides what you set in fw_WeaponBoxSpawn.
But, when you manually drop the weapon the piece of code I'm talking about is missing(probably wanted?), so you are lucky and it somehow works.
If you still don't get it, here is the order of calls.
When you drop a weapon:
1."drop" command is send.
2.DropPlayerItem() is called.
3.weaponbox entity is created.
4.Spawn is called.
5.SetModel() set the entity model to models/w_weaponbox.mdl
6.Touch() is called -> here you should set the new weaponbox life.
When game drop a weapon:
1.PackDeadPlayerItems is called.
2.weaponbox entity is created.
3.Spawn is called.
4.SetModel() set the entity model to models/w_weaponbox.mdl
5.Think is set to CWeaponBox::Kill, so it will later remove the entity.
6.pev_nextthink is set to gametime() + 120
7.Touch() is called -> here you should set the new weaponbox life.
If you do it like that then it will work also in CS and probably other mods.
Short story: Set nextthink in Touch, not Spawn so game won't override your value.
2.In fw_WeaponBoxThink use charsmax() to retrieve a string size.
3.In fw_FadeOut also check if entity is valid. Some other plugins may remove it while the task is running.
You could retrieve pev_renderamt inside fw_FadeOut, instead of passing it in set_task(so you will pass only entity index) and you won't need to convert the value to integer anymore. Anyway, your way is ok too I guess.
4.Don't remove weaponbox entities like you do. That way you only remove the box and not the weapon that is inside it.
The correct way to remove it is to call think on the entity. Since your superceded Think(), you could set a custom value in a unused field, like pev_iuser3. In fw_WeaponBoxThink, check pev_iuser3. If it holds your custom value, then do nothing. Else, set the properties(as you already do) and supercede.