A lot of people now seem to leave themselves 'reliant' upon E.H.U... Which means a lot of lovely sites and pitches without 'hook up' are lost to them.
I'd keep your options open, perhaps use an E.H.U. in Spring/Autumn when the nights can be colder (and longer!).
In Summer you'll have the choice of some lovely, unspoilt, secluded pitches that don't have E.H.U. points, if you're happy to use a battery and or gas...
I have an EHU and a power pack, the power pack takes 3 pin plugs etc.
If you use the power pack for tv, dvd player or lights it should last a weekend, if using on a fridge it will last around 7 hours. Power packs generally are more suited to lighter tasks, but are a useful alternative if arriving onsite without EHU.
The EHU can be left on all day to keep the fridge cool, and has the extra benefit of powering heaters etc.
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.