Hello there,
Was at the GDSF last year with the MH, and I would recommend this is the way to go. I have attended before, and used tents, and bed and breakfast accommodation on different years. Not been for a few years, but the show is very BIG, and there is quite a bit of walking if you want to see it all. If you are off site, there is quite a bit of queuing to get in or out of the car-parks, plus if its wet well you know what happens then.
If you book in advance, it can be a lot cheaper, and your right in the middle of the action. As for food and drinks its the usual rip, but when I mention this to stall holders, they quote high rates to get the pitch there. Personally we came back to the MH for our meals, plus a bit of a sit-down, and unload the 'purchases'. The show has night time entertainment, but this finishes at a senseable time, and it is quiet overnight, and well patrolled.
Best of luck if you decide to go, its a great show...