suffixes - What's the reading of -中 as a suffix?

I see this all the time, but I don't know that I've heard it spoken.

For example: インストール中

Is it simply "なか"?

Answer

The reading when used as a suffix in this case is ちゅう (the on-yomi of the character 中)

So インストール中 is pronounced インストールちゅう. The meaning is "installing", or "in the process of installation".

More generally, 〜中 used in this way can be thought to mean "in the process of ~"

Edit: There is another possible usage of 〜中 which Hyperworm describes in their answer.