The fender mic'd to 0.046-0.049, depending on the location- close enough for 18 ga. I'm still looking for some 18 ga, and may end up taking apart something in the house. We had a city-wide power outage yesterday, so traffic lights were down, and I couldn't make it in time to get any welding gas either. This is about the way things go when you actually HAVE time to do something...
A 19 ga sheet- as mentioned- would probably be perfect but I have never seen that size; never looked either. I did bend a single piece of the 16 ga just to see how it would go. It isn't pretty, but I would use it if this was a tractor or something. I'll use it to estimate size needed.
How far off (+/-") is within margin for the patch metal?
Brad