Read more on the manual, it says "within 80 feet" - bought a Heath/Zenith yard light from Homeless Despot a few years ago, claimed 100 foot range - got within 10 feet of it thru a single pane glass window before it worked. Took it back. YMMV is definitely at work here...
If the hole in metal wall is close to YOU(and the remote fob) then 4-6 inches square should negate the "Faraday cage" effect. If the genny is what's close to wall, probably a couple FEET square (centered on the receiver)
Dan's thought might be worth looking at, the manual describes the remote as being modular but doesn't go into much detail. It also doesn't give frequency, just that it's FCC listed.
It does, however, make me think that if you want the remote to work you should leave a trickle charger on the battery (powered from (too wimpy to run a welder) line supply - because in order for the remote to work at all, the battery has to be on (couple switches on the genny control panel) which would drain the battery if you kept in a "ready to start remotely" mode for more than maybe a couple days.
Oh, and my neurons are still OK, I just tend to them "fizzling" if I'm not sure the particular idea might not work :laughing:...Steve