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It's only hard if you want to re-use the tub, otherwise just tear the fuckers off. You want to get as much of the residue left behind off as you can, so getting a tub glue removing compound is worthwhile in my experience.
Tape is way easier to apply (and far less time consuming) than glue. It won't give quite as good a bond, but as I assume these are mainly for flat time trials then you should be fine with tape.
Also, how hard is removing old tubs and mounting new ones? Should I use glue or tape?