I would leave the actual weight and dimensions as they are in their ProductVariant fields. UPS/UPS2 will use the weight to calculate rates.
Instead, product dimensions could live in ExtensionData as an XML node. There have been several discussions here in the forums about using well-formed XML data in ExtensionData field.
At the dimensions you mention, 24 x 19 x 19, the product will likely be subject to dimensional weight. The total square inches equal 8,664. That volume is currently divided by 194 to yield 45 lbs. in dimensional weight. I understand that is what UPS charges. I am currently experimenting with dimensional weight to get a more accurate rate from UPS through ASPDNSF.
ASPDNSF appears to ignore dimensions or the number of boxes at the moment. So the closest tool would be dimensional weight--only when larger than the actual weight.
The divisor for UPS will change to 166 from 194 on January 3, 2011. Dimensional weight will increase as a result, and the threshold for dimensional billing will come down for shipments to Canada.
MSx 9.2, SQL Server 2005, Windows 2008 R2 Web 64-Bit