There are pros and cons to each. Exposure to dampness is not an issue. They are marinized, spark arrested, and designed for that environment. It is part of the anchoring system, and assumes the anchor and line will be in the water and inserted into the anchor locker wet.
Horizontal: Above Deck (easy to access and maintain, however it can clutter a small foredeck); Small deck hawse(hole) for line; Rode only goes around gypsy 1/4 turn before sending rode into the anchor locker.
Vertical: Below deck (less clutter on foredeck, however is limited to the available space in anchor locker); Consumes additional anchor locker space; Rode goes 1/2 way around gypsy before sending rode into the anchor locker; Requires a larger hole in the deck for the mechanicals to pass through.
IMHO, this comes down to available space in the anchor locker. Do you anchor is deep water, or have relatively heavy ground tackle? If you're just looking to burn some money, how are the rest of your accessories? (TV, Stereo, GPS, Radar, etc)?
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