well, one way is this: you start a script when someone triggers that specific trigger and that script constantly checks who enters it's area. when the unit you want to give weapons to enters the area it gives them to it.
set triggers activation to anybody ( or if the specific unit is on either side set the activation side accordingly)
this goes to the triggers on activation field:
[unitname, triggername] exec "check_certain_unit.sqs" (presumes that unitname is a global variable, triggername is the name of this trigger)
in check_certain_unit.sqs:
_unit = _this select 0
_area = _this select 1
#loop
?_unit in list _area: goto "give_weapons"
~1 ( set delay to anything u like)
goto "loop"
#give_weapons
(in here you do all that is needed to give weapons for the unit)
;then exit
exit
this script is reuseable, so you can make many areas that gives weapons to different units if u like.. hope this will help in a way or another.. I haven't checked my code, but hope it's not too much bugged ;)