Hey,
I've taken a look at your cad files, this first I would suggest is that (if possible as you aren’t using AutoCAD) you try to use polylines over lines and join them together. This is just good CAD work flow and it will make it easier for you when it comes to sharing drawings and importing into SU.
The second thing is, I see that you have several designs in one file. I create a special SU cad file that is separate from the design file, this allows me to cut, flatten and prepare the .dwg for import to SU without having to ruin the design file.
Now in the prep for import you need to remember a few key things.
One: All the lines look the same once they are in SU so make sure that one the lines that are important are there, get rid of any unnecessary lines like construction lines and layer properly.
Two: Hatches don’t come into SU and from the drawing package you use are converted into blocks, either delete them as you will find a lovely texture to put in their place.
Three: Make sure you don’t have any lines tracing each other; SU doesn’t like it when two lines occupy the same space. So if you have any duplicates tracing the same path delete them.
Fourth: If you are new to SU I would make sure everything is flat, SU does 3D better than and CAD programme I’ve come across.
Ok now into SU,
First thing you do is the go to model info and purge the unnecessary data that you could remove in the drawing package. AutoCAD has a habit of adding layers that aren’t needed.
Second select everything and then intersect with selected, SU 7 does this automatically when you are drawing a line but you need to do this with imports.
Then select all again and use the make faces tool, I’ve found that with SU 7 the Make faces 1.1 plugin works where the 1.4? (I think that’s the name) doesn’t.
That is all i can think off right now I hope it helps