same

Sorry for the late response, but here's how:

First, make sure each map is published in the workshop, each map is set to public, and each friend is subscribed to each map. Then, host a game and before inviting your friends, press Esc, then go to Game Options > Maps and click the square to the left of "CustomOnline" until it is white. Make sure each square next to each map is white, too. Then invite your friends and custom maps will be enabled in the map rotation.