Acad drawing elements are unlike other Cad applications. In Acad, a line can be a simple 3d line, or rectangle with thickness, and extrusion direction (vector). A acad line with a thickness of 0.0 is a line, with a thickness of 1 inch, it is a rectangle with a height of 1 inch. You can not make a line with thickness in SketchUp. The SketchUp importer changes a line with thickness into a face. In SketchUp, when you model a set of connected edges in the x,y plane(say a polyline), then you loft the edges in the z direction, Sketchup will change the connected line into connected faces, and edges. SketchUp's DXF exporter will not translate this model into a polyline with thickness. The following is a portion of an ASCII DXF with some of my notes prefaced with #. A DXF listing always starts with a group code then followed by the data. This sequence is repeated throughout. Thickness, and bulge are as the tables above indicates. Some of the group codes are documented under "common group codes for entities".
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0 #Acad group code precedes every piece of data
POLYLINE #data is entity Name
5 #Acad group code for handle
29 #handle
8 #Acad group code for layer name
T-2DPLINE-3 #layer name
62 #etc.
5 #etc.
66
1
10 #Acad group code for x
0.0 #x
20 #Acad group code for y
0.0 #y
30 #Acad group code for z
0.0 #z
39 #Acad group code for thickness
2.4332129974000671 #thickness
40
2.0
0
VERTEX #first vertex in polyline
5
34
8
T-2DPLINE-3
62
5
10
-1.3768750602197291
20
-3.437321703110606
30
0.0
0
VERTEX #second vertex in ployline
5
35
8
T-2DPLINE-3
62
5
10
-0.8415682007917144
20
3.2296819097655769
30
0.0
42 #Acad group code for bulge
-0.9902342116099923 #bulge data
0
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I do not know what AutoCad drawing elements require entity thickness, width, and bulge. At one time Acad dimension line arrow heads used a lwpolyline with width, but I do not know if Acad 2011 continues to do so.
My copy of Volo View is good up to Acad 2000. Thanks for the info on TrueView. Had it on my system at one time, but didn't like, and removed it.