Your Heartland measures just over 19' long, 8' wide and 9-1/2' tall, and the perfect cover for you is the Adco SFS AquaShed Cover for Travel Trailer # 290-52240 which is designed to fit 18' - 20' trailers, has zippered entry doors should you need to access your trailer with the cover on and has cinching systems to ensure a snug fit.
You could also use the Classic # 052963731637 which has a 3 year warranty and elastic corners for quick fitting like a fitted sheet on a mattress.
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