Anyone install a circulating block heater?

What:
I'm contemplating installing a circulating "bottle" block heater on both my Avalon Hybrid and my Gen 2 Prius. One that's 1,500W.

Why:
Because

1. It's more efficient to heat up quickly in a few minutes than to be releasing heat into the atmosphere all night.
2. I at times forget to plug in. Either that or the GFI pops when least expected from capacitance of cords lying on the ground. At any rate, if I have an hour to get going there's no point in plugging in the stock heater. But a higher power heater would make a difference in as little as 15 minutes.
3. It gets really cold here. Like -40⁰ cold. And the stock block heater just isn't enough to make that much of a difference even plugged in all night. A couple hours on a 1,500W heater could make it blow warm air from the start.

Question:
I just can't find any info of anyone who has installed one in a hybrid. I had one on my 1984 VW Golf and another on my 1993 Mazda 323 and loved them. Any suggestions of what hoses to connect to?