The Apache was not designed to carry pax on the FABs/EFABs, that capability has come about because of tactical need. If you ride on the left side there are step/handles that are used to climb up on top to inspect the rotorhead to which you attach yourself. They are very strong and can carry a load if needed. If you sit on the right side the only place to latch on to is a handle used to climb up on the FAB/EFAB and is of much lighter construction. I have seen one break when a maintainer climbed up to work in the cockpit(he was quite large though).
The proper technique is to sit with your back against the fuselage, sort of tucked behind the nose gearbox on the engine and to brace your feet against the Hellfire racks. It is easier on a Longbow because of the wider EFABs.
FAB- Forward Avionics Bay
EFAB- Extended " " "