I would try
http://www.overtons.com They have many covers that are "custom sized" for most Four Winns Models
But you could also consider the FourWinns cover if it's in your budget:
I have the factory cover for my H240, and it is very nice and covers to just below the rub-rail all the way around. Uses two posts to support the middle areas, and has kept the boat very dry. Not meant to be left on while trailering. Mine came with the boat I purchased used, however a few months ago I called a FourWinns dealer to check what the cost of this cover is, and it was around $700. Not too bad considering a top notch aftermarket cover could be around $600
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"Knot Easy" 2000 Horizon 240 Volvo 5.7GS /SX
tow: 2017 Honda PILOT EXL-AWD
prev. boats:
'87 Chaparral 198CXL 4.3 OMC Cobra
'69 Jetstar 16ft Ski Boat, 115hp Yamaha
'68 Aluminum Jon Boat, 3hp Sears
'64 Water Wings