TBH, the Gumball works because of the clientel, ie, older generation with money and the cars. The MKII Golf GTI really are owned by the younger generation of whom alot are still at college or university. So money is the issue rather than the reluctance to take part. Although I suspect that more than 10 should be able to make it, but it would take some planning and a definate date to be set well in advance so that those who wish to go, can make arrangements with their respective work for the required time off.
It may also be worth contacting the venue to see if group discounts are available. The more entries, the less it costs. That will attract more people too.
As for accomodation, well DH obviously has the experience there, but each to their own. If you want to find a camp site, then go for it. If not, then hotels are the way to go and DH has the info. As long as the 'rally' goers all pitch up at the ring at the same time, it shouldn't matter who stays where and it should be a blast.
The bickering on this thread is ridiculous, and just damages the chances of a potentially, really good event.