WWI 15.17 Totals has something to say that might be of use to you, allowing you to simplify and genericize the definition of the phrase:
To decide what weight is the laden weight of (T - thing): [see WWI 15.17 Totals]
decide on total weight of things enclosed by T plus weight of T.
The total of... phrase is one of the many built-in conveniences for frequently-occurring tasks.
FYI, a phrase can be used in much the same way that a property could be, so I’m not sure that you absolutely need the every turn rule. Every use of laden weight of... will prompt a calculation when the value is needed.