Annnd in keeping with the rule that you can't make something work until you ask someone to look over your shoulder, I've solved this.
For anyone stumbling on this in the future, once the Inventory tab is filled out and the Item listed is set to 'Equipped' the Total weight carried cell updates and becomes your Fatigue. In this case Weight is the same as Encumbrance.
I suppose to handle Fatigue from Travel you can add an 'Item' called 'Fatigue from Travel' and update it as this increases?
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