Wino, I don't know about the A300 but to cycle the gear doors on a 747 on the ground is not that simple and would take a long time to accomplish at the ramp. You would have to get a ground engineer to manually open four gear doors after depressurizing hydraulic systems 1 and 4 and re-pressurize to close the doors after inspection. Totally impractical to catch the stowaway that boards during taxi or at the holding point.
Planting an explosive device in a wheel well would by no means be a "non event" but apart from loss of hydraulics, fuel tank rupture, spar damage would in most likelyhood result in wing seperation. R.I.P.