Assume for the sake of argument that the tubing is rigid and there is no risk of blowout. How likely am I to get that to fit?
I think you might have to try different tubing (assuming you're talking about vinyl/nylon tubing) to see if you can find one with slightly oversized measurements. I know 8mm tubing is a tight fit on 8mm fittings. The internal o rings are large enough to cope with slight variances but the plastic internal housing was quite tight on tolerances, in the 8mm size anyway.
Not sure then. I'll find an 8mm fitting and dismantle it to remind me again how it fits together and holds the tubing.
Judging it by eye and using an 8mm fitting as an example I think it would be borderline but might just do it. There's around 1mm or less of the o ring standing proud of the internal tube.