[orange4boy]

Yes, the engine and transaxle get to ambient overnight without the blanket and sealing. I have to get busy and post some pics. Think of you engine bay like an inverted grocery floor freezer. The hot air rises and gets trapped in the engine compartment if it can't escape through any holes in the top. The opposite of a freezer where the cold air sinks. It helps to have a belly pan bit isn't essential unless it's windy. I used my face to feel for warm leaks.

I learned from building my house that tiny leaks can cause a lot of air to escape over time. If you have them, eliminating air leaks is way more important than improving insulation and leaving the air leaks.

There are two external plastic coolant pumps on the 2000-2003 prius and three on the 2004-2009. (one for the coolant thermos) The best one for your use would probably be the cabin heat/heater core pump. It has a one way valve and it's meant for full temperature and pressure. It's probably cheaper than the inverter pump which is often replaced around 100,000 miles. It sits under the inverter and is easy to identify from the 5/8" ID hoses coming off it. The inverter pump is in front of the inverter behind the driver headlight.