Rust/scal *inside* rocker panel - 98 Cabrio

My wife's Cabrio convertible has a weird 'leak'-- actually the problem is that it isn't leaking enough.
It appears that the design* allows for rain to run off the top and
inside the fenders to the rocker panel where it is drained out through weep holes. The weep holes are clogged with rust & scale- so the rocker panels fill up, and the water runs under the back seat, then to the floorboards.
I've been able to clear them by spraying water up through them and they are good for the next rain, but re-clog almost immediately.
My next thought is to open a sizeable hole in a wheelwell [both front and rear?] so I can pressure wash the interior of the rocker panel. The rocker panels are in excellent shape- feel good and solid- the problem seems to be all on the inside. [possible that these are covers, covering up the original drainage?]
*This may not be the original design, as the car has been painted & I have no idea what bodywork might have been done.
Any thoughts on the best way to drain these permanently?
thanks, Jim
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