Has club moved on?

You need to click on the membership section top left tool bar. Contacts for centres, rallies etc are listed there. Also look under "what's on" for other events and pop up sites.

The other club, C&Cc run Temporary Holiday Sites on a much bigger scale often without the need to book. This might be what you are looking for?

This club don’t have the basic THS’s like the Camping and Caravanning Club.  Just these reasonably expensive pop up campsites.LINK

Hi, I doubt many would claim that it’s a doddle to find info, at times I resort to Google rather than the sites search facility however, if you are interested in rallies the club offerings, via centres, often provide opportunities to stay at much reduced rates on decent sites.

If it’s the field with tap and elsan pit type site you are after then most likely c&cc is a better bet.

Our MH friends have attended hundreds of such events over the years but now not so many.

Just Google CAMC Rallies. So easy that even I can do it. 

Due to Covid restrictions it hasn't been quite as easy to book rallies etc this year. We're booked in for one but the deposit hasn't been taken yet. The ones we prefer are not on sites and with both clubs they have the usual  water and disposal points and usually in interesting places where normal camping access is restricted.

Do rallies last for more than 4/5 days? This is specified in the OP

I get the feeling that, as suggested by others, the OP is thinking of the THS offered by the other club.

Yes I was able to read what the OP specified - and of course there are holiday rallies lasting more than 4/5 days and organised by several CAMC centres.

Quite possibly by the other club you mean the Camping and Caravanning Club and I suspect the OP is looking for;

Temporary Holiday Sites

We have used these in the past and found them to be good value and good fun.

We've been on rallies that are run for two weeks by one centre and then continued by another centre for a further two weeks. You can choose your length of stay with either centre. I don't think we've done more than a week ourselves but many spend the summer months "on the circuit." (travelling all over the UK and of course abroad in normal circumstances.) 

Rally affiicionados know the system.