I tryed to make mesh pants first!
ABOUT MESH PANTS VIEWER
Mesh item needs the viewer corresponding to using a mesh.
The official viewers 2 and 3 or some third party viewers.
Please see an official site for details. (https://secondlife.com/support/downloads/)
ABOUT MESH SIZE
Rigged mesh items are can not resize.
I made and include some sizes according to various Shape.
Please wear the thing near your Shape, And wear an alpha mask too. It hides original Shape.
and please try to DEMO first.