I'm sorry, I wasn't clear.
I initialize my H2H room on my laptop (almost any old PC or Laptop will work even w/o a graphics card) and leave it running 24/7.
Then when I want to play in the MA, AvA or SEA, I use my main PC, launch AH and join whichever arena I want. No issue.
Except if I want to join my H2H room using my good equipment, I must exit the laptop version, as AH won't let you log into an arena twice with the same account. Then you can join your room and afterward, switch and join with your laptop again to keep it running.
I'm up to about 4 regular players after 90 days and probably 30 or 40 unique IDs crossing my roster from time to time. It's all about consistency!
If my European players didn't see a H2H room up every time they look, they'll quit looking so...
Around the first of each month, MS or AH, whatever, will try to update and shuts the room down. It's not without maintenance requirements but for most of the month it's stable.
Of course, if you expect people to like an MA or special events map for H2H with only 2 or 3 other players you probably shouldn't bother.