Thats very unusual that your agency is letting you use your personal vehicle as part of a sec convoy. Even as a chase vehicle which is also unusual for a sec convoy (the tactical mind set is usually to get the client away from the threat). Each vehicle is usually four seaters (to accomodate the min standard two agents + the VIP) so that each one can be used incase any number of the convoy vehicles is/are disabled. Not to mention that Z being a poor choice with it's poor rear visibility (tactically speaking) and low seating position. Steering wheel to weapon transition must be a biotch.
as an example:
YouTube - Vehicle Tactics P-3
edit: Sorry I'm saying chase when I'm thinking pursuit (car).