Dow Corning is the way to go and i have never been let down with its results.
It will be fine to use when sealing between panel and floor as well.
If the stuff taht you used previously dried out and cracked it would suggest that you have used the incorrect compound, maybe used a decoraters caulk?
If you use Dow Corning stuff you should be fine and as previously stated make sure that the bath is full so as to compensate for movement caused by weight.
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