Canesisters,
I am so sorry for being so neglectful about responding! I just finished nursing school and had no time for anything else over the last couple of years (minus this amazing project which served as a great procrastination fix).
I know it's way too late, but for anyone else who may be wondering (and so that I feel a little less flaky), I will reply now to your questions.
How did it work out?: It worked out pretty well over the summer and it is still functioning as additional space for the ladies to roam in.
Weeds: Unfortunately (and fortunately some of the time), our land is covered in blackberries and wild roses, which take over if you don't stay on top of it. I'm afraid the chickens don't eat these plants, and I may need to hire some goats sometime for that job, but until then, there are portions of the tunnel that they don't seem to go through because of the areas that are harder to prune or dig out. On the other hand, there is a chance that they may wander into those bushes for shade when it is hot. So, currently about 3/4 of the tunnel is pretty clear and they do use it. In the areas they do roam, they do eat most of the weeds. I have a feeling I would be doing a lot more weed shoveling around the border of my garden, if it weren't for this system.
Bugs: I don't have a huge bug problem in the first place, but I think this system may help some with bugs. I know the chickens will eat them when they see them. If my strawberries or tomatoes touch the ground, it seem that something eats parts of the fruit, so it is not a 100% fix.
Access to moat: As for access to the moat, I haven't made much of an effort, but if I wanted to open up part of it, I would just clip the hog rings that hold the fencing together and open it, then reseal it when I am done.
Overall: I really like this system and I would recommend it to anyone. If you have really stubborn weeds, consider digging them out by their roots prior to establishing the tunnel, especially if they are thorny weeds like blackberries or roses.
Question for you!
I love the sound of your plan! Did you carry it out? How did it work for you?