I own a 20′ Lund Alaskan tiller. I paid $800 for a custom snap cover in 2005. I travel about 3000 miles per year with my snap cover. My comments:
1) Buy heavy fabric in lighter color to fight the sun damage over time.
2) Vents at each pole are key to let out moisture.
3) Install male side of snap outside the boat and on the underside of the gunwale. Prevents smashing snap at dockside.
4) Incorporate vents or holes of some sort at each place your boat has a rope tie-down. This allows you to install the cover at dockside and still have it roped to the dock.
5) Make cover snap along backside of transom splash-pan.
6) Do not incorporate motor cover into boat cover. Make a separate cover for motor due to ease of installing boat cover at dockside overnight.
7) Make sure your the guy you hire to make the cover measures the rig with chairs and gear installed in the rig or risk having a “conflict” with placement of support poles of cover with chairs, downriggers, GPS, sonar, cables, etc.
Tightlines,
PFG1