Thanks for the questions, Martin.
Yes, the enclosure dampens sound a great deal... you can have a normal tone conversation with it running nearby. It's nowhere near silent, but it does kill just about all the high-pitched whine from the router.
As for heat, the router will get warm from running so long, but I use a shop-vac on a reduced speed (using a router speed control) to capture the powder-fine dust, so the air ends up being circulated out of the chamber over time as it operates.
I will be moving to a full dust collection system when I move (4", high flow dust suction at back of cabinet with inlets cut in a row across the front to keep airflow moving over the table toward the rear)... and that will definitely keep the air circulating and fresh.