Amp rig in SKB or Gator rack case. How much “U” do I need?

Building a new rig in either a Gator or SKB rack case. Trying not to under or over size on the build. 4U sees compact, do I need 6U or 8U for the near future.

I currently have a Orange gain baby 100 which is 2U and a Furman rack conditioner which is 1U