Welcome to the forum Mitch.
FYI these "salvage title insurance site:airforums.com" search results may unearth some helpful posts here on AF:
Unfortunately I don't see any bright lights above.
Have you discussed the details with Progressive? Even if they value the trailer as worth "zero dollars" will they still issue you a policy to cover liability etc. when you are towing the trailer? This is crucial IMO.
Dollars and cents:
-- Was your purchase price lower because of the salvage title?
-- What is the market value of the trailer, as a functional 2006 28' ?
-- Can you live with "losing" the value of the trailer, if there is an accident and the company does not reimburse you for the lost trailer?
-- What are the alternatives?