What makes it harder in practice vs theory is that:
1) importing the Pictures BLURS everything so I have a hard time guessing the actual center line. Wrong measurements add up over time in construction and you see it here as squares fail to align.
2) The PNG files of the are pictures and their Border is the Anchor and thus the isometric Gridlines actually get in the way, yet I still need the grid lines because of issue no. 1. (measurements are wrong over distance).
This is an MGT2 ship - modified Fat Trader with 2x the engineering tonnage (from 19 to 44), 2x the fuel (40 to 80), less than half the cargo capacity (200 to 90), 3 less rooms for Workshop and Med Bay, Thrust-6, a lot of suites, 3 turrets and 1 barbette.
Mongoose Traveller gives you the Isometric PNG files to do this. You can import it in Inkscape. there is a way to do this efficiently which I'm discovering.