I have an unmodified RAI on my Disco 3 and after considering the Safari unit came to the conclusion that the RAI was just as effective without being modified based on the following points.
If the vehicle is moving the system is unlikely to ingest water through an unsealed RAI as the holes are there to ensure that any water in the system drains out.
If the vehicle is stationary in deep water for any long period of time where the airbox might fill up with water you are most likely going to be stopped by water in the electrics anyway.
The design of the stock intake is such that the bow wave drops away under it and the only time that you may have a problem is if you are in a fast running deep stream where the water "piles up " against the drivers guard. the RAI does a good job of preventing this scenario.
I'd be interested to hear from someone who had access to the design work on the RAI as I reckon it's designed to do its job and maybe the people who advocate sealing it up are in some ways defeating the design objectives.
There are some pretty good videos on youtube of vehicles windscreen deep fording with no issues with RAIs.
Regards,
Tote

