Welding trim holes in bed

[ItWillBeSlow]

I may be buying a bed that requires some trim holes to be welded up in the bed.

I am comfortable with a welder and prefer to use a small magnetic copper backer to fill open holes. I can’t tell if there is adequate space to get anything in between the bed skins to put the copper backer on the backside of the hole?

Has anyone done this? If not, what method should I use? Weld a nail head in?