@mac7595 Thanks so much for your reply. Unfortunately I am not able to open the file you have attached:
In regards to some of your points I am planning to print this on a low-end kit 3D printer I have built Prusa i3. I have looked into getting my model(s) printed and it wasn’t cost effective for me 
As I am unable to open/view your file could you maybe help advise me with some of your points so I can attempt to make these changes myself?
Suggest you change the display precision. ← How do I do this?
There are some small dimension errors in you model ← Could you elaborate as I have viewed in wire-frame and cannot see what might be wrong?
Is the internal box part of what you plane to print or is that just to establish the envelope of the cover? ← Not quite sure what you mean by this. Everything in this model I had planned on printing.
Thanks again for you help and would appreciate feedback.
Alex
Alex info
Suggestions;
Unit display precision to at least .xxx;
Deselect snapping;
Deselect color by axis, only shows parallel not on dwg axis use inference engine ;
Keep entity info open per TIGs suggestion in SCF. As noted in attached it reports diff lengths on right vs left;
Build vol for RepRap is 200x200 mm if memory is correct. Just FYI you can scale up and down to fit.
As noted some time copy & move out edges helps find problems when faces not forming. because of required modeling tolerance. You will think closed loop but not really;
As noted before for your machine and use of FDM has possible issue with building unsupported structure. Link I post has info to help you under stand. Slicer can add infill to help also.
board3dcover_mac1_2014.skp (76.8 KB)
Additional Info; Selecting back face: Then select option align view gives view perpendicular longitudinally of item. Doing that you can see the non symmetry so, cut in 1/2 and mirrored so both sides are the same.
050216_1400_mac1_2014.skp (65.3 KB)
Good Luck
@mac7595 Thanks so much for you help with this. Sorry for the late reply not had a chance all week to get back on and tinker.
The files have been super useful and I really appreciate it. In regards to some of your setting recommendations I am struggling to understand them to be honest:
“Deselect color by axis, only shows parallel not on dwg axis use inference engine ;
Keep entity info open per TIGs suggestion in SCF. As noted in attached it reports diff lengths on right vs left;”
I have made this model a lot larger as I read somewhere it is best to build larger and then shrink down. Id planned on scaling down to 0.1 before print. In regards to moving out edges I can see the benefit in doing this but am worried as I cannot always get the edges back in the same position they where.
When I print I had planned on printing on its flat end and using support in Cura/Slicer to help.
In regards to symmetry your last file you posted have you made the symmetrical changes for this? If so could you please tell me how you have found that the model is not symmetrical. I have looked and when I was building I was very concious to make sure it was symmetrical. I would love to know where I went wrong and how I can see this for myself as when I look at my model it appear to be symmetrical to me (taking measurements etc).
Thanks again,
Alex
Yes, I used a section plane down middle to cut model in 1/2 and then mirrored the one side to make total model. I came to conclusion it was not symmetrical by using entity info on like entities and obtained different answers. AS check the back face was selected, then align view which gives normal view of that surface. again things did not look same so decided to mirror.
Be aware when you are scaling the wall thickness also gets scaled so you need to account for that in your design.
Color by axis can be helpful tool tip but only means line is parallel to axis not “on drawing axis”