I looked at all the linked threads about the single-arm mirrors breaking. I remain convinced they can be repaired to full functionality by epoxying a threaded repair "bushing" inside the door-mounted piece and using a nut to tighten the arm, spring and retainer back into original position. Especially if I read the digital caliper in one of the pix as 0.67-inches, just over 5/8". If that approx 5/8" inside diameter is right, there's room for a 3/8" pipe nipple and that would offer plenty of strength to the repair.
I wonder if there's a longer version of Gotsmart's pickup-style mirrors.
Just be careful of the model year issue around 2002-2003 Fords as mentioned earlier. What Gotsmart has on his 2004 chassis might not match the OP's rig if the chassis under his "2003 coach" is actually a 2002 Ford chassis.