How does the unit perform in an extreme environment - dusty, hot (Building site environment) ?

Will go for the diskless Lite PC2 unit, add SSD and deploy with heat sink.

I would appreciate any feedback on the extreme environment suitability.

Also Ideally I need a AUTO ON version of the Fit-PC2 Lite version with SSD which ignores the ON/OFF switch. What is the lead time on the AUTO ON version of the fit-PC2 Lite diskless?

So if power is available then the units starts. I would like to bypass the ON/OFF switch in case it is accidentally pressed in the field.
Is it possible to bypass ON/OFF switch?

fit-PC2 works well outdoors in Nevada summer, outdoor in New Delhi and on arctic cruises. It is not affected by dust at all. Overall I expect you to be satisfied with the robustness.
All units are auto-on for a year now.
There is no support for bypassing power-button. You can take the cap off or cover/glue it so it is not pushed accidentally.