Answer: a lot.

I'm a clutz with hand tools. Drilling holes for rivets and driving rivets in hard places taxes my technique. Occasionally, after several attempts each a rivet size larger, I run out of rivet sizes and have to use a structural bolt. A tin airplane can get heavy that way.

I can confirm, having lost a few round inspection covers in flight I did not fall out of the sky

Given the controversy when gopros first came out, I also found it amusing that this plane not only had a gopro attached to it, but it was on a mini-tripod and attached with rubberbands. Still took 60+ holes to make the thing unflyable.