Guessing you have a car that has not been restored in that area nor coated if it had been. Also assume that its all together and the option is not high on your list to remove the lower dash and deal with it out of the car.
Just thinking of what I might try - but if anyone has done it leaving the panel in place feel free to jump in and add your experiences - good or bad
Without removing the panel I think I would first pull the seats and remove the front carpet section and underlayment. Good time to look for that buildsheet
Then treat the bare metal surface that you can reach with Evapo Rust in soaked small shop towels. Some of the rust converters might work OK but they may not reach inside the overlapping panels that make up the bottom edge of the lower dash. You may choose to remove some of the switches (ignition, lights ...) for better access and coverage
Then rise or leave depending on product used and apply a protective coating to as much as you can reach. Think your going to find that the humid climate and its affects are going to be an ongoing challenge but will leave suggestions on how to address those challenges since I haven't had to live with them just deal with them later
Good luck with the project
