Are water trampolines as difficult to insure as backyard trampolines?

I found out that homeowners policies do not cover water trampolines on the lake, because they are not "on" your property. The insurance company also will not cancel your policy, like they will if you have a backyard trampoline, as it represents no liability to them (again, its not "on" your property). However, you will be with no coverage on the water trampoline (umbrella policies do not cover as an umbrella is additional coverage to your insured/insurable property). So if anyone gets hurt at your house on your water trampoline, you are on your own to foot the bills!