All umbrella policies that I've seen require everything you have to be insured with the same insurer (personal home, rental property, car, etc.). In my case, for whatever reason, it's cheaper to have one company insure the rental property and another my own home, car, etc. So, I instead have $1M of coverage for each rental property on that policy. The cost for $1M of liability instead of $300k is something like $25/year (per property).