I assume you have an Awlgrip finish on your spar.

If you do a Google Search on "Awlgrip AND Shrink Wrap", you'll come-up with a variety of manufacturer and other warnings.

I personally would guess that the lifting would exacerbated IF you have a black or dark spar vs. a light colored one because of the heat as well as the moiture. (If you try and put your hand on a black or dark colored spar in the sunlight -- even in the cold winter, you'll probably burn your hand except in VERY cold weather.) It certainly is test to the finish because of the thermal shock of being the sun and not in the sun with the addition of "moisture".

Since a canvas cover (properly padded) hasn't caused problems, I'd tend to use the same sort of details in the vicinity of the mast. Sunbrella with some suitable chafe lining seems to provide the proper combination of "breathability" or localized ventilation. You can tie it to avoid movement (and attendant chaffe). Then you can deal with the transition to your "TARP" -- which probalby isn't white.

My concern with your situation, Larry, is how you are handling the relatively large deck situation on your multihull vs. a normal monohull. You have more concerns with lift, etc?