I was really hoping you could offer pole heights and if PVC is a worthwhile idea.
9 hours…yikes! I can appreciate that not happening right away. Sounds like you’ll be good to go by next season when you’d actually use them in season, so that’s good.
Poles are adjustable, and heights will vary by boat model/lenth/layout as well as age and “stretch” of mooring cover. Thus, pretty individualized. People could probably chime in and be in the ballpark, but you need to get it taunt, so slight differences would matter - particularly in winter with possible snow weight and sag if not precise.
For height measurement you are looking for: I would recommended taking a pole that fits in vent slot for the normal adjustable poll. Have one person push up until cover is taunt. Other person tape measure that precise height. To be accurate at each spot, you’d likely need someone else to push up at previous spot, while repeating this process at each of the other spots. This is because being taunt in one spot, pulls and impacts other pole heights at the other air vent locations.
I hate to say it, but if you want to be precise, it’d likely take this sort of process.
Finally, overall some sort of PVC support skeleton should work. Some people build their own PVC or Wood frames. Others go some sort of purchasable route like shown in the post above. If going that route, I’d strap/wrap some heavy duty tarps or after market all season cover over it all, as again, the OEM morning cover is not really built for that kind of winter weathering over time.
All of that said, I think shrink wrap would be a much better winterization process for sealing it up more thoroughly (for winter, snow, pest incursions, etc) AND being winter weathering ready.
Given the cost of these boats, I’m one to error on the side of caution in these upkeep areas.