Really the only way to control line width in exported raster images is to change the export size. The smaller the exported image, the thicker the lines will appear. You can adjust profile edge weight in Styles but that only deals with some of the edges. You might play with the Straight Line styles and see if they provide you with something use can use.

The alternative would be to spring for the Pro version so you can export vector lines and adjust their weight in some other application or go through LayOut.
Screen Size--1550 px Wide
800 px Wide
Straight Lines 0.2pix Exported at 1550 px wide
Straight Lines 0.4pix Eported at 1550 px Wide

Ok! Very cool videos Jeff and Dave! 👍

But sorry for this time in this particular case...
I believe that I am more speedy and more simple! 💚

You right I use plugin but just one and indispensable in the Toolbox! 😎
The genious Inverse Selection by TIG! By Right Click 👍

Only curvated face is duplicated not the volume!
Inverseselection.jpg

Edit : I verify this morning because that was just theoric this night! 😄
One of the curvated face must be "inverse white / blue" and the 2 curvated faces must be "Intersect with the model" ! And of course Rectangle Selection must be left to right! 🤓

aasol.jpg

Don't forget that in the past I have made "speedy challenge" Sketchup / Moi3D
"without plugin" 🤓
(of course I have losted at each time because Moi is unbeatable! 😒
It's maybe for that I use now plugins! 💚 :

If you are interested : Moi 22 seconds by PaQ! 😲 SU 40 seconds and playing as Horowitz! 😄

http://moi3d.com/forum/get_attachment.php?webtag=MOI&hash=c1961cccf715ed10247d21984cc1bc51&filename=testsk01.jpg

Hi Dave, thanks for responding - I think I have found (part of) my problem, scaling. The original was quite small (about 4cm across), so I scaled up by a factor of 10 and then 100. I then played with the offset parameter in the RoundCorner extension, and by reducing it I seem to avoid deleting faces. Appreciate you taking the time to offer help - I'm sure I'll be back!