Hello Rob,
My slide toppers awnings are not covered on my Landmark; I am not aware of any Heartland product with metal covering the slide topper tube. I believe the topper awnings are Dometic.
I am aware of the carefree of colorado brand topper (
Carefree SideOut Kover III) that do have a metal cover option.
Hope this helps. Possibly others with more information will chime in here....
Brian
EDIT: Dometic does have a slide topper with metal cover -->
Slide Topper Full Cover. As well it suggests a FC (Full Cover kit) can be purchased from a dealer (possibly Heartland) to cover an existing slide topper. Call your dealer or Heartland and they may be able to help.