Sorry it's been a while. I forgot to check in! We did flaming bowling balls a few days ago and it went awesome. Indeed, launching fire never gets boring.
https://www.youtube.com/watch?v=d1fniKBMuLQI have definitely thought about throwing clay pots. In fact, I emailed some professors in ceramics at my local university a few months ago, wondering if they wanted to make pots to throw with the trebuchet. None of them responded and I haven't followed up. I'm still thinking about clay pots. Wondering if I can make myself some kind of substitute by molding plaster around a balloon. It needs to be something strong enough that it would survive launch (for sure) but would break on impact. Could fill it with all kinds of things and then use the usual technique to set it on fire.
I haven't done pots yet mainly because it would be a lot of work and expense and would need a lot of trial shots and testing. I would want to launch, say, pots filled with water, to make sure it all works for certain before I ever dared to launch pots filled with gas.
To protect the ropes, I simply dunk the sling in a five-gallon bucket of water before each shot. The manila rope, when wet, really doesn't burn or char -- it just gets some black discoloration. The sling has held up fine. I should take some pictures of it next time I'm out there.
I actually tried putting out our campfire next to the trebuchet with a wool blanket a while ago and I burned a big hole in the blanket. I think the coals were too hot. I hear that wool blankets are good for putting out fires but there must be some details I'm missing. That was my first time trying to do that.