Oppy, you are allowed to ride on the fire trails etc but do not get caught digging or making anything otherwise 4 figure fines could be applicable. I will check up for you about vehicle confiscation laws too, as they are applicable under some circumstances in national parks.
Oppy, look up BFP on the net and then get into the legislation area, do's don'ts etc and the range of offences and the fines available. Hell of a lot of reading but basically it is an offence to take or possess an 'appliance' on BFP land, appliance includes shovels, mattocks etc. Offence to dig on BFP land without permit etc.
Is it worth it?
Build at the Park seems like the best idea.