yeah thats the go, thats what ive done with mine. Also to help more people fit on the track at once move the berms out a bit n widen the shit outa the jumps!

crazy-latin-stevin has the right idea, puttin things under the dirt as fill. 44 gallon drums are gun for up ramps and pallets are the go for downys! Both are pretty easy to get, just head round to your industrial estate and ask around and they generally cant wait to give them to you!

Good luck with it bro!