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I recommend using the Camco UltraGuard Pop-Up Camper Cover for your application. According to my research your 2018 Somerset E3 Camper is 12' long but I wasn't sure if that included the tongue and deck or not so you'll want to measure what you're wanting to cover and choose either part # CAM45763 which is 12'-14' long or the part # CAM45764 which is 14'-16' long.
Please note that covers are designed to cover the box only so you'll have a bit of slack when you... view full answer...