I was wondering if anyone used a CB400T for a real long trip and I am curious about their experience.

So much depends on how your bike's been looked after in all those years. If it's been stood for ages, check on all rubber components like carb diaphragms, o-rings and so on. As others have also said, the size is fine for rural Euro touring. I hope it was cheap!

I bought one new in must have been '78 - looks much like yours - and despatched on it one bad winter. So not a long trip but a lot of miles. The expression 'boringly reliable' springs to mind, as so many Hondas of that era. I think at the time my rationale was to buy a 'sensible work' bike after running MZs and Bonnevilles, but I went a bit too far.
The brakes were not so hot, nor was the suspension (CX500 era) - in fact nothing was, but it never failed.
I see now from my teenage bike log it was so 'boringly reliable' I sold it after just 3 months for no good reason - and bought another MZ.

Two years later I had the automatic version of the 400T (looks the same; 2 speed), much nicer for work but I recall the bolts that attached the rear sprocket to the cush drive used to sheer, until I welded the sprocket on. I am sure that must have been due to the clutchless gearchange, but it's something you might look at on your manual model. Same engine, I did 40,000km before I couldn't bear it any more. No probs or wear at all besides that sprok. Got the older 350K4 later, now that was a nice bike in a bendy sort of way.

My recollection of the 400/4 was one of the best-looking bikes of the 70s - until I actually rode one. What a disappointment - a bit like marrying Suzi Quattro. But to be fair I think I'm not a multi kind of guy.

Chris S