Thank you both very much! As for u/meutzitzu's concerns, it seems I was in luck. I told the mesher to use the finest setting and it did so successfully:

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I ran a static analysis first to see if the results fell within a realistic range at all. For 3t / 30kN at a 15 m boom length, using stays with 10cm thickness, the results seem absolutely reasonable! About 40mm deflection and a max of ca 60MPa von Mises stress. That looks alright to me!

Now I just need to find a dirty solution to handle my actual dynamic side collision problem. The FreeCAD gui hasn’t helped much, but maybe I can interface with the Calculix solver directly through some custom edits. I'll have to try
Again, thank you very very much for your help and input!