Yes, a metal working shop would do a great job, even to just cut a hole in the side panel. But, I was thinking to do it myself. It's a fun project and the good thing is that a Cooler Master HAF XB side panel is € 8 on-line, should I destroy mine in the process

All I really need to go down to the quite remarkable 29/30 °C is, I believe, a square air intake the size of a 12 cm fan, approximately. I am thinking of a 12x12 or 10x10 square hole.

That is a relatively simple thing to do with a dremel and some patience. It won't have super round edges, but I am planning to use some rubber finishing all along the edges. Possibly not the very best and most elegant solution, but I liked it when I did it in the past.

Mark, the air-tube is going to be difficult because of all the cabling around the drives, I am afraid.