If you are importing these from other file types make sure you get the options 'units' set right.
For example, importing in 'mm' when the original file is in 'm' will make the SKP model 1/1000 its proper size - Sketchup/OpenGL can't create very tiny facets, so some bits might be 'lost' in translation.
Similarly importing in 'm' when it's originally in 'mm' can have the equivalent issue, with very enormous geometry failing to form too.
Assuming the Units size is correct...
The clipping-plane issue can also results from having geometry that is far away from the model's origin.
Importing a DWG/DXF and 'keeping the origin' in the import-options can put the imported objects miles from the origin, then OpenGL can fail to render it properly.
Even if you import CAD data ignoring the CAD-origin then it can still have issues.
For example, if a 'Block' has been made in the CAD file it is imported as a 'Component' in the SKP.
That Component's origin is the same as the Block's.
Some sloppy CAD users make blocks in their files with the geometry miles from [0,0,0], BUT accept [0,0,0] as the Block's origin.
Therefore although the Component's geometry appears near the SKP origin its insertion-point id miles away - this has the same clipping-plane effect since the bounds of the model are unnecessarily enlarged.
Zoom Extents will show weird model bounds issues.
This can be resolved by using Model Info > Components > Show axes ON.
You might see axes-markers miles away from the origin...
Select an imported Component-instance, right-click context-menu and use 'Change Axes', pick a new logical insertion point for the axes, probably on the object's geometry corner etc.
Changing the insertion point does not shift existing instances, but new ones will now attach to the cursor sensibly as you place them...
Recheck with Zoom Extents and/or the clipping-plane issue... if it still exists try changing the axes of other components until all are sensibly located and the issue is abated.
