Not sure that anything with wheels is the answer - apart from a 4x4 offroad vehicle. Grass and rough terrain render small wheels near useless, and you end up dragging the thing more than rolling it. I learned this from giving my daughter rides on her wheeled toys when she was a toddler. My 5x4 all-metal technical camera folds up and fits in a smallish canvas gadget bag. The bag will also take a couple of DDSs, a lightmeter, folded darkcloth and cable-release. Apart from weighing slightly more, it's no more inconvenient to carry than a DSLR kit. The real pain is the tripod, but it doesn't have to be monstrous. A Manfrotto 055 is adequate, and is about the minimum I'd consider for useful stability with any camera. No matter what size. I don't know what the total weight is, but it's not so excessive that a few miles walk isn't too taxing. I suspect the unseen TV cameraman accompanying any wildlife presenter lugs a lot more, and a lot further.