Well, I wouldn't walk across an Undercover. They are just not that strong IMO.
I would also not want to walk across one of the fiberglass painted to match tonneaus i.e. Leer , ARE.
If you are looking for hard covers that will support weight, I would look at Bak industries or Extang. Extang makes what they call a Solid Fold. It is a tri folding hard cover that will support 200lbs. Easy to take on and off and looks better than the Undercovr IMO. Bak makes the Bakflip G2. Also a her folding cover.
If you want one that is hard, lays flush with the top of the bedrails and rolls up into a box behind the cab, look at the Roll'n'Lock.
None of these will lock like the Leer or Undercover, but if you have a locking tailgate, then they are locked. If you want one of these and don't have a locking tailgate, you can get a Pop n Lock for like 40-50 bux
Hope that helps