World of Warcraft players, come in!

yeah, he's probably doing it wrong.

I will lvl my rogue the next week, and see how it goes with the pickpocket glyph (and I might lvl up eng to have the remote mailbox so when I have my bags full, send all the boxes to my paladin)

what lvl you think it would be doable to farm the boxes with safety?

Well, assuming nothing really changed, "Tyr's hand" is still the best place to farm lockboxes IMO. It's where I farmed all my lockboxes and the route is big enough to where you can endlessly farm lockboxes until your bags get filled to the brim.
Although I would recommend not doing much of the EPL quests, if any, due to possible phasing in Tyr's Hand that can severely cripple your PickPocket opportunities.
50/60/70 would probably be the best shot you have since EPL is only a 40-45 range now. Highly recommended being in a sub spec for faster stealthing and whatnot.

Since you're gonna be doing this over the next few days / weeks, here's a couple macros that helped me and hopefully they'll help you as well.

Sap + Pickpocket Macro. Way outdated (TargetNearestDistance doesn't work / exist), but still works like a charm.

#showtooltip Pick Pocket
/cleartarget
/console targetNearestDistance 5.000000
/targetenemy [noharm][dead]
/console targetNearestDistance 10.000000
/cast [harm,nodead] Sap
/script SetAutoLootDefault(1)
/cast Pick pocket

Macro to throw away most excess trash from Pickpocketing

/run f=string.find;for b=0,4 do for s=1,32 do n=GetContainerItemLink(b,s);if n and(f(n,"Homemade Cherry Pie")or f(n,"Hickory Pipe")or f(n,"Alterac Swiss")or f(n,"Superior Healing Potion")) then PickupContainerItem(b,s);DeleteCursorItem();end;end;end