Thank you for the replies and emails, it seems this is a bit like oil and tyre pressure threads, there are many varying opinions.
Many people have used a cover of one sort or another but few have ever removed them for inspection or cleaning. In my case it was 10 years ago I fitted my RIF covers, I treated the whole area with Waxoyl and then ACF-50, sealed all the edges with a high performance, heat proof, elastic recovery non shrinking sealant.
Four years ago I removed the covers, air lined them out, jet washed them, treated with Keronite and then Waxoyl, ACF-50 ect. There was not much in the way of solid matter in there but what was in there was very wet (before using the jet wash 😬) even though the car had been sitting in the garage for 4 weeks without an engine in it. Now four years later the engine is out again (don’t ask 😔) and the findings are exactly the same and again the car has not been used since the L2B which was a dry day.
So my theory and that of some others is that you will never totally eliminate water, salt and small debris from entering this area for various reasons, side skin and chassis flexing, ingress from between the bottom chassis rail and the bottom edge of the skin, the difficulty in sealing the lower end of the cover because this is where the diagonal chassis member joint with the lower rail is (standard S3 chassis) etc. etc. etc.
So if you cannot eliminate ingress completely, would in not be best (as ozzy said) to leave it open? This is the theory of some including me, if it is left open hot air would be passing through drying out the debris, if they are dry they are going to cause a lot less corrosion than wet derbies resting against the ali skin for weeks or months in the case of the sorning brigade, on end. Leaving them open would also facilitate easier regular cleaning out, re treating with whatever takes your fancy.
This is only my personal opinion based on my experience, my not so lateral thinking and the experiences of others who I have spoken to. Nothing more than that.
Guy
(Edited as I cannot spell Waxoyl) 😳
Edited by - Guy Lowe on 11 Dec 2013 11:20:40