Okay, so I've asked and asked but noone has any old skateboards so I decided to go ahead and try to make a tracking dolly without them: to be honest Im not sure yet how the 'track' part is going to work out (I'm thinking of doing an L shaped wooden track about 3m long). So far I've made the 'dolly' and added a couple of fixtures to retain the tripod and I'm really pleased with the result - it runs on small fixed castors which are a little noisy/vibey on hard surfaces but work great on carpet. When the track part is sorted it shouldn't matter what surface it's on as the wheels will run along a guided track, if all else fails I'll swap the castors out for something smoother. Total cost was around £11 and took about an hour to assemble - there are loads of video tutorials on You Tube (Indy Mogul is best) if you want to make one. See you Monday!