Box it in with an outline
Get one clean outline that follows the parts at a set distance.
1
Start with the artwork you want a border around.
2
A single outline is drawn at a fixed distance around everything selected.
3
Cut the outline and the artwork comes off as one piece with an even margin.
Every setting
1What each number in the dialog means, and where it starts.
Distance
How far outside the shapes to draw the outline (mm)
What it is
Stretches one outline round everything selected, like a rubber band, then pushes it out by the distance you set. Hollows and inside corners get bridged over rather than followed.