If you right click a part on Cad-mep and select cadmep properties and then select the costing tab it will show the total weight of the item but that includes the flanges and seams.

I do not use CAD-mep much but it has the same built in reporting that Camduct and ESTduct has and you should be able to utilize or create a report that will do what you want. just right click on the screen and select reports. video link below on how to set these up

just be careful as there are several ways to report weight and some will give you full weight including insulation, flanges etc or you can just report on the main body material weight including or excluding seams.

try these out and should explain it a bit better than me - 

Reporting with Fabrication CADmep - YouTube

Help | Autodesk

Hope that helps you