I’m heading off to the Ardennes in Belgium on the 8th and have booked my bike on the Eurostar assembled. Has anyone done this before? All I could find with the search was tales of boxed etc. If so, any recommendations?

Yes, I have.
London to Brussels.

No problems at all.

Its a different company that handle all of the freight.
You need to drop it off a few hours before you depart and the place is hidden at the back of St Pancras, which can take a bit of finding.
Then just pick it up at the other end.

Good stuff. That’s what I was hoping! I’ll try and find that place in advance just so there is no faffing on the morning. It’s an early start.

I've done it twice.

Once no problem, second time the bike didn't arrive.

They said "no problem, just come back tomorrow" which obviously but a massive spanner in my works/plans.

After much good natured and hilarious banter it transpired that it was my fault all along for not getting the bike there early enough (though earlier than I was told I needed to get it there) and thus it missed the train I was on.

So I'd recommend being extra early with the bike drop-off just to ensure it's waiting nicely for you at the other end.

During the booking process they kept saying 90 minutes. I was hoping that would be enough but maybe I should give them 120 to be safe.