The gathering works great, but bags are easily filled. I've ticked off "smelting" in the general settings but does not seem to do so. Any suggestions on how to get the smelting to work?

Hello, do you have add the name of items at smelting (in advanced general settings tab 'Looting & farm...').

I don't see any fields for smelting, other than the checkbox. 

I see:
Don't harvest objects
Harvest objects
Prospecting List
Milling List

Can't see any "Smelting List"

Yes sorry, you don't need to add items names (this feature is rarely used, i had forgotten how to use it). 
You need to add in your NPC DB (tab 'tools') (or in your profile) npc type "Smelting" (WRobot read only position of this npc, in game select npc near smelting zone).