enhance your metalworking skills by making your own brackets
out of aluminum . . . once you get the hang of it, you will not
need any "store bought" brackets in your future.
the 1/8" angle or square tube can easily be cut with a jig saw,
skil saw, hack saw, etc - whatever works best for you.
and yes, with a few select cuts, an 18" length can wrap around
compound curves and fastened with your choice of fasteners.
since 99% of them will not be showing, they don't have to be pretty.
If you have a chop saw with a wood blade & carbide teeth,
you can cut up a coffee can full of different sizes in just a few minutes.
(you can not cut non-ferrous metals with a general metal cutting blade
on a chop saw - it will gum up the cutting edge with molten metal).
To fully understand the physical chemical collaboration
between dissimilar metals, ...... A quick Google Search
can give you an insight of what NOT to use on a metal structure and "why".
https://www.galvanizeit.org/design-and-fabrication/design-considerations/dissimilar-metals-in-contact
https://www.preservationscience.com/materials/metals/PGC.html
and, probably one of the most controversially debated subjects on this forum is
the use of pressure treated plywood for decks and lumber for bracing.
Corrosion of metal Panels and Trim in Contact with Treated Wood
Do not allow aluminum, aluminum-coated, and galvalume-coated panels and trim to come into direct contact
with wood preservatives containing copper, mercury, or fluorides. Avoid direct contact between bare metal
panels and treated lumber where condensation will frequently form on the metal surface in contact with the lumber,
and where the wood treatment is more noble than the metal surface.
Use an appropriate barrier to separate metal panels and treated lumber.
.