If its known to be busy,personally I just wait to get handed over from one station,flick the frequency change button,get to within a couple of miles of the boundry and orbit until you recieve the OK.
Have a very good friend who got into alot of trouble for something that happened earlier in the thread..for..
1)Going into the zone without clearance,presuming all okay..and to top that,
2)Used his GPS as primary navigation and in defiance of being told not allowed to transit the zone,skimmed along the boundry using his GPS map..and it was wrong,he slipped inside.
The authorities had a field day with him.