This is one of the more complicated set ups. See the figure below for an example set up.

Build the Helm's Deep keep first.

This should be a well-fortified bunker that is easily defendable by only a few people. The attackers should not be able to flank around the back side of the bunker. The best way to handle this is probably to call areas to the side of the bunker out of bounds.
Helms Deep is essentially two bunkers, the "keep" and "outer wall". The keep should comprise a third of the bunkers length and be on the right side. I suggest first starting with the "keep" as everything basically revolves around this. Remember that the outer wall will not always be in place so the defenders need to be able to defend only using the part of the bunker known as the keep.
Place a flag bin (and optional bell) at the foot of the front of the keep and designate it as the main gate.
Designate on area behind the keep as the defender's respawn.

Build the outer wall

You will need to find some barriers that are easily laid flat or moved out of the way. These should act as the outer wall. The outer wall should make up about two thirds of the bunker and should be to the left of the keep.
If you are going to allow players to pass through the outer wall once it is blown up then only a section of the wall needs the ability to lay flat or move. If you don't allow players to pass through the wall then I suggest making the entire wall moveable.

Build the rest of the field

Mark off a path to the main gate of the keep and designate it as the ramp. The ramp should not have very much cover. The ramp doesn't actually need to be a hill although if you can incorporate a hill that might make things more fun.
Around the mid-point of the outer wall, mark off a small area and designate it as the water gate.
Set up bunkers surrounding Helm's deep but leave a decent amount of open space that the attackers must traverse in order to reach the Helm's Deep bunker.
At the attackers respawn place the bomb (plastic bin), torch (rod) and flag bin with 20 flags.

Dividing up teams

The preferred method is to have about 1/3 of the players act as defenders and the remaining players act as attackers.
Generally the defender's use high rate of fire blasters and the attackers get springers

Maryland Foam Tournament 2025 Field