I have read much about the underside rust problems associated with earlier MX5 models. Can anyone give any guidance as to whether this is regarded as a serious problem with later models please? The MK 4 referred to above seems to be in excellent condition so I am wondering if Mazda have actually improved the rust protection on more recent models? Can anybody advise me on this one. Help will be appreciated

Too early to say if its an actual problem or not. There were many posts here detailing the complete lack of rust proofing on these cars.

I have just done a 30th Anniversary car with Dinitrol and Bilthamber products yesterdayand also did my 2018 car and have done another few ND cars when they came out in 2015.

I have also done a a good few NC cars.

No the NC and ND are no better protected.

My mk1 1990 is better protected with its original protection than my mk3.75 2014, personally I think the newer cars are worse.