Honu,
I had some initial concerns - and I certainly would never weld on galvanized metal, but I've yet to experience any problems with a few coals or a few sticks of firewood in a galvanized tub. In fact, when I first built my tripod firepot (galvanized 16" feed pan), I intended to burn off the coating and apply BBQ paint instead. The problem was that I couldn't get it hot enough to burn the coating.
I think the thing is that it doesn't actually get that hot. With a few coals for dutch oven cooking, my pan can even be touched on the sides with bare skin. With as big a fire as would be safe for the size of the container, it gets hot, but after a dozen+ burns, I see no change in the galvanizing coating, (unlike with the much higher heat of welding), so I'm thinking that in this application, the risk of gaseous ZnO is relatively small.
You're right of course, that for ultimate safety, one would need to acid-strip the galvanizing off and re-paint, but adding those nasty chemicals to the mix sort of defeats the purpose of using a $5 feed pan to keep the fire off the ground. If you have strong concerns, stick to using a small BBQ grill or the like...