We used to have Allstate for everything and don't think our premium was nearly that much....thinking more like less than $100 per 6 months. Then Allstate started playing games so we moved to Farm Bureau for everything. Our premium for the trailer is $86 per 6 months.
With your auto coverage, the trailer is covered while being towed. With the homeowner, the contents are covered. Suggest you go back to the agent and find out if that figure is really correct and why.
So much with insurance depends on the area you're in. That may be part of it, but I'd try to dig a bit deeper before paying that premium. Oh, BTW, welcome to the forum! And happy camping!!