[Wesley221]

pawn Code:

new UnderCoverobj[3];
UnderCoverobj[0] = CreateDynamicObject(18646,0,0,0,0,0,0);
UnderCoverObj[1] = CreateDynamicObject(18646,0,0,0,0,0,0);
AttachObjectToVehicle(UnderCoverobj[0], GetPlayerVehicleID(playerid), -0.5, -0.2, 0.8, 2.0, 2.0, 3.0);
AttachObjectToVehicle(UnderCoverobj[1], GetPlayerVehicleID(playerid), -0.5, -0.2, 0.8, 2.0, 2.0, 3.0);

You have to create the object before you can attach it. And i dont think this can be done through PVars.