Forever at Half-Mast (experimental sonnet rhyme scheme included)

[milo]

Thanks so much for all the suggestions! Here's my first edit:
I think I am a flag, forever at

so, the break on "at" annoys me for several reasons and it may just be pickiness but:
1.  It is considered bad form to break on inconsequential words (articles, preps, etc.) unless trying to draw attention to them.  This doesn't seem to be the case here.
2.  You are attempting to rhyme a non-accented syllable with an accented syllable.  Is it possible to promote "at"?  Possibly, depending on the wrods around it.  Let's see how one would read this:
Forever at half mast
forEV erat HALFMAST
so, the meter ends up being off as well leaving
3.  The line is iambic tetrameter with a hypermetric ending and an odd dactylic sub.

half-mast, and drooping in a windless dusk,
hung scarcely twitching like a crumpled husk
when corn-worms, swollen, slow, and waxy-fat
creep out of their exhausted habitat,
to unfurl on their journey to the sky.

This sentence comparing yourself to a flag is impossibly long and hopelessly convoluted.  A sentence should have a purpose.  This was supposed to explain how you think you are like a flag and ends describing corn worms which in turn only relate to the flag through it being like a husk.  The last three lines here describe corn worms.  What do they have to do with your central metaphor?

A flag whose destiny's to never fly,
but watch the sun go down below the flat,
unending earth, and tremble at my doom-

your circular comparisons have turned in on themselves - by referring to yourself in the third person as a flag you are left as a flag observing your own doom in the third person.

the hopeless night, and then be lowered down…
and folded up, and placed into my tomb:
an unmarked box, kept in an empty room,
an unremembered shelf, an unknown town,
and leave a naked rod stuck in the ground.

I have a particular distaste for ellipses in poetry, especially improperly typed ellipses.  It shouldn't matter but my distaste is shared by most of the poetry loving community to the point that ellipses are used to satirize beginning writers.
I don't really understand how your "doom" could be the hopeless night.  Perhaps your "fate"?  It is difficult to reconcile the hopeless night as "doom".
I think you are missing "on" before unremembered shelf (and why should shelves be remembered?) as otherwise you are saying you are placed "in" a shelf.
Overall, i think it is a nice concept.  The meter is mostly good.  The metaphor is sound.