One way to guarantee sufficient numbers is to include the Nats results into your club championship pointscore
If the Nats are in NSW the Heaven / Norths riders count it as a pointscore round which at somewhere like Lakes would mean lots of entrants This way riders of lesser ability may not figure in the Nats trophies but they may just advance their points enough to figure in their own clubs results. The same goes for Vic and Qld.
Interest in a National Title should not be garnered on an Internet forum. It should be done at club level with questions like, You wanna ride the Nats, How many laps, You want camping, Where you wanna ride?, 1st choice, 2nd choice etc.
This information is compiled in the first 6 months of the year ( Is May too early to run a title event as , say for Heaven members it will only be the second time out on a bike in competition ) with deposits taken from all participants and both submitted to MA to put together a fruitful proposal to clubs to tender from.
Just my 2c worth