Some folks fail to realize the tire blowing or loosing a tread normally isn't the most expensive part of that tire failure. It is the residual damage done to the trailer, lost fenders, sewer lines or power lines or flooring damage. Plus the possibility of having that tire fail when your on a highway putting you and family in harms way having that tire changed. Many folks have already experienced the 5 or 6 year old tires failing and I would suggest the same as the other, pull them off and replace. Putting a listing on Craig's list for used tires may recoup a portion of your costs on the new tires.I know the local landscape guys are always buying used tires for the trailers they run around with. Not much weight and your tires on that type of trailer could run till they are bald with no issue.