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Guys do that and add a drain hole/hose/tube perpendicular to the lowest point.
If you were doing it custom,
like fiberglassing in fg tube with and fairing it all bitchin with paint,
it'd look clean.
If you get capped holders that have a tube hose clamped on and then sealed on the vertical rail,
that'd work but not look as trick.
Easy to justify on a beater,
not so much on a survivor...
TP