Piping mass properties for mobile hydraulic hose and tube assemblies

It seems there are two ways that Creo can calculate mass properties of hose and tube assemblies. One is using WT_LEN and the other is by assigning a material (.mtl) in the line stock file. The config option piping_material_source can be set to weight_length or material_dir to control which way it works.  Which method are folks using for mobile hydraulics? It seems like wt_len works well for hoses but the material method might work better for tubes. We are having a bit of trouble with mass properties of some piping assys changing on us after multiple regenerations or re-opening the assy.  In either case it seems like a material should not be assigned to the pipe part in the piping assy. Is that correct? Does anyone have a list pros/cons for which way to set up piping_material_source or other tips for using Creo to do mobile hydraulics?

We are on Creo 2.0 at the moment.