Here are 2 examble pics of my actualy print object.
Normaly I print with 6 perimerters and have no problems with this and there is no gap in the wall of 3 mm by 0.60mm nozzel, extrusionwidth 0.72mm
The main-reason ist the fact, a constructed wall has always an inner and an outer side. Therefore the number of perimeters down to 1 cause always 2 perimeters, one inside and one outside.
The space between this 2 perimeters will be filled
when External Infill is set to Rectilinear like Viceman's question
and
when External Infill is set to Concentric the infill-perimeters fill the gap in dependence of the wall width up to full-infill or let a gap that is than filled with this wobbeling print, Viceman fears.
For both it applies the infill-perimeters are part of solid layers (green colored)
At last here is a pic of my normal print with 6 perimeters. Remark please that you can only see 2 (two) perimeters thats makes 4 lines together. 2 perimeters inside and 2 perimeters outside. The light-blue perimeter ist in contrary to the above green infill part of "Inner-Perimeters".