Several threads on this already. Research 'stated value' vs 'agreed value'. Stated value may be cheaper but prepare to fight to prove your trailer is worth more than the 2700 that NADA says it's worth.
I got an agreed value policy through Josh Pagel at FCIS JPagel@fcisinsurance.com
, they can write for Progressive. Yes, you need an appraisal (a little over $200), I got mine from James Polk who has lots of Airstream appraisal experience, firstname.lastname@example.org
Best of luck, depends how much money you have in the trailer as to how you want to insure it.