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
https://bathroomrepairtutor.com/courses/how-to-remodel-a-tub-shower-combo-platinum/acrylic-tub-installation/
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