Never been to Blackberry lane but have camped at several sites on the Island and they all have charging facilities and blackberry lane have previously said they had on their website.  Don't worry about it, just ask in pubs/cafes etc and they will usually let you plug in, I think the Sure shop in the grandstand let my mate charge up there once.
The valuables are a bit more difficult, I've always just left my stuff in the tent and never had any bother but there have been growing reports of petty thefts from campsites so I would be a bit cautious, the only lockers I know about are in the ferry terminal which at least is open about 20 hours a day but it isn't ideal.

Look the rule on the Island is this - if you have a problem, any problem just tell a manxie,  in a pub, a shop in the street, in a taxi anywhere, sooner or later one of them will sort you out its just the manx way.

 In my youth in the days before we had cash points four of us walked into the little cafe which used to be in the entrance to the shopping centre up near the archibald knox ordered breakfast and then discovered it was a bank holiday so our trip to the bank to cash a cheque was off and we were skint, the lady owner lent us £20 which we returned after the bank reopened, mind you it was 1978 and beer was 28p a pint (half the price 'across') and fish and chips in onchan was about 60p!! 
The reason you probably won't get much response from Regency is that they are gradually winding up the business, would have thought the glamping company would help you looking at their prices!