Might be able to do a quick thing on that later. What I'd reccomend first is to pull apart an existing map which has it, like the hub area of the new campaign.
To do that find the .hwm file in Hammerwatch/levels/ and copy it into the editor/ folder. In this case copy campaign2.hwm into the editor/ folder. After that click on the address bar of the editor/ folder, the whole C:/program files......editor/ all that, and copy it. Next open up the command prompt for windows, the little black box thing. This can be done by hitting start andtyping in "cmd" and hitting enter, or by finding its icon.
With the command prompt open type in
cd "
Then right click on the command prompt, hit paste, and then put another quote mark, so it ends up looking like
cd "C:/...something something...editor/"
Then hit enter, this takes the command prompt to your editor folder, then we can use the ResourceExtractor to unpack the campaign, as such
ResourceExtractor map campaign2.hwm
After this you should have a new folder called campaign2/, feel free to dig through the levels and learn from how the real pros did it.