Vue.js 2.x - Vuetify 2.6.4 - v-data-table v-text-field Validation rules applied to sum of values of multiple fields

Question

I need to validate the size of a box and have 3 fields:

Width, Length and Height

I solved as per this codepen

Now I have to add a further rule: "sum of sides" i.e: the sum of Width + Length + Height

I create the variable containing the limits:

sos:{"min":20,"max":45},

But I really do not have any Idea of how apply to the project keeping the same structure..

Can somebody suggest the right Direction?

Thanks