Here is the completed upper arm with elastic fabric with male snaps inserted in three places to secure to the Bicep Armor, the Shoulder Armor and to the Connecting Bridge. The elastic fabric is pulled through the gap under the Shim Strip in the ridge line channel, then connected to the Bicep Armor snap.
Credit goes to OBI-WAN'S JEDI ACADEMY for the idea of the Shim Strip in the Shoulder Armor.