I have shipped guns for umpteen times over twenty years in a aluminum gun case without any attempt to disguise it. Pretty obvious it's a gun. So far never a hiccup in delivery. Maybe potential USPS sticky hands have avoided it thinking it may be a setup? Dunno. Hardly ever buy insurance, preferring to self insure. But I'm not shipping Purdeys, etc., either.

When an old man dies a library burns to the ground. (Old African proverb)