this is set to use one package for the entire order.
The UPS Rate request requires the dimensions, it will fail if you dont pass packaging dimensions.
with different size products you would be better setting it to use a package for each item, and add the product dimensions through the add to cart buttons.
create new cart columns for width height and length, and in the add to cart buttons, set these for the individual products, then on the confirm page, double click the UPS Shipping server behavior to edit it, and bind the dimensions to the new cart columns.