Yeah, unfortunately it won’t be as easy as attaching some XP values to a box.
For one, you will need to mark the the box as “hostile” of some sort. Not too hostile, though, otherwise your wipmpier hearthlings will start running away from the sight of it, thinking that it’s an actual enemy. Recall that you already can attack inanimate objects in Stonehearth; your soldiers destroy the camp of the Goblins when you send them all in. It would probably be a good idea to have a look at how Radiant made those attackable objects in their code, and adapt that code to your problem.
Assuming you got this first step to work, now, when the box gets destroyed, it might reward some experience. And at this point, you might say you have a full, complete mod. You can set up a dummy, as soon as it’s up, your soldiers will run up to it, swarm it, and reduce it to splinters, and get some XP. You will have a working, but extremely unrealistic mod.
In order to make an attackable dummy that isn’t destructible, you will need to take the following things into account: a) Hearthlings attack an enemy until either it dies, they die, or they take so much damage that they’re forced to run away. Your engagement time with the dummy must be on some sort of time limit, otherwise your soldiers will always keep hitting the dummy and never backing off, b) with the normal Combat Component, you only get XP when the enemy is killed. So you’ll either need to write a custom component for your box that sends out an “Oh no I’m dead” signal after a few hits, and your footman can relax, get his xp, and not attack the dummy anymore, which, although it sent that signal out, isn’t actually dead! Heehee, aren’t we such scamps, OR you will have to create your very own new action chain, not the usual
attack_enemy or whatever they have, but
train_on_dummy that will consider this, c) unless you manually break your soldiers apart into parties, all your combat hearthlings will travel and fight in a party. Attacking a dummy shouldn’t be a party action, it’s an individual action.
Considering all of these facts, I want to direct you to
stonehearth/components/party_component. You will almost certainly have to write your own component for the dummy, whether you do it the easy way or the hard way, so you might as well get comfortable with component composition.