TT this year..............
Hi Flyer, Hope you make it, it really is worth the trip.
Now for details: Most places on the course are simply a matter of turn up, sit and watch the racing, although there are a few places that charge for seating etc. Have you considered signing on as a marshal? Just turn up at the hut behind the grandstand and offer your services. That will get you access to some great viewing points, but will also put you in contact with some of the nices, most helpful people on the island, who may be happy to help with lifts to your marshalling point etc.
As for camping in a field, I guess it's the same as anywhere else, if you pitch your tent in someone else's field then you may get woken by an irate farmer. It may be worth considering a "proper" campsite (last year I think I paid about £ 7.00 a day at Union Mills). The Union Mills site is on a bus route in and out of Douglas, and perhaps more important, is right on the edge of the circuit (Peer over the hedge to watch practice sessions etc.), and close to a really good pub (The Railway at Union Mills) where you can order Pizza from Douglas to be delivered.
I'm sure you'll have a good time, let us know if you are going, I may do it myself at short notice.
All the best,