​I like using punch slugs to fill holes. The Roper Whitney Jr. hand punch is a great tool , easy to change out punch sizes, not too expensive at flee markets, or on line. Also good for punching holes in flanges to plug weld. Goes up to 1/4" diameter punch size.
The punch slug is slightly smaller than the punch size. once the slug is in place hammer it back flat and it is trapped in the hole so it won't move during welding.
These holes were 3/16" diameter so I could have filled it with filler rod but this method is much easier to weld and since it is close to the edge eliminates the chance of having the edge melt away. This method also minimizes any warpage and eliminates the need to grind the weld.
Holes gone, these were planished and sanded with 100 grit roto lock disk on cordless drill.
This was a fun quick project, Just needed a project that was not long and drawn out. Frank