what kind of flexible tubing are you referring to? I think the biggest challenge with something flexible is keep everything at the proper pitch when set horizontally.
If you are only referring to the overflow portion of tub, I would recommend installing the drain assembly before setting the tub. this way you can make the connection having the tub at eye level than trying to connect in a cramped space.
If you haven’t already check out this tutorial and around the 8 minute mark in video I go over installing the drain assembly before setting tub