NEC doesn't agree with that, no exceptions written for "watertightness". Does the shift from 40 A base ampacity (THWN-2) to 35 amp base ampacity (THWN) even matter for you? If you do the calculations for THWN and it comes out OK, then just document the change and calculations in your plans and you should be OK.
300.9 Raceways in Wet Locations Abovegrade.
Where raceways are installed in wet locations abovegrade, the interior of these raceways shall be considered to be a wet location. Insulated conductors and cables installed in raceways in wet locations abovegrade shall comply with 310.10(C).
Where raceways are installed in wet locations abovegrade, the interior of these raceways shall be considered to be a wet location. Insulated conductors and cables installed in raceways in wet locations abovegrade shall comply with 310.10(C).
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