Even though caravans almost never bring wagons anymore, you can still use the trick of having only a single point on the map edge where a wagon can enter and reach your trade depot from to force caravans to enter the map where you choose.
First, build your trade depot, above or below ground but preferably near a map edge. Usually it won't matter which edge, but sometimes you will have an embark location where caravans will only enter from one side of the map. Then dig or clear a 3 tile wide corridor to the map edge. Either dig it underground and ramp it up to the surface near the edge, or clear out trees and boulders and build side walls to protect a 3 wide path along the surface. Near the edge of the map things get more difficult because you can't build walls within 5 spaces of the edge of the map. You can however build drawbridges, and raise them to form walls.
The finished safe entrance will look like this:
WWWWWWWWW
W W
BBBBBWWWWWWWWWWWWWWWWWWWW DDDDD W
+++++++++++++++++++++++++ DDDDD W
+++++++++++++++++++++++++ DDDDD W
+++++++++++++++++++++++++ DDDDD W
BBBBBWWWWWWWWWWWWWWWWWWWW DDDDD W
W W
WWWWWWWWW
where the left edge is the edge of the map, B is a raised drawbridge, + is a smooth ground, floor, road, or other surface wagons can travel over, W is wall, and D is your trade depot. Make sure there are no other 3 tile wide paths from the map edge to your depot, and trade caravans will always spawn at the safe walled-off spot on the map edge.
Also, hammerdwarves are useless in 31.0x. Make axedwarves instead.