From my observations the best way to combat this is to get out there and ride responsibly.
Traditionaly anti groups of users are more antagonistic towards MTB'ers and dog walkers than trailbikers in SDNP.
This has much to do with the mean level of trailbiking standard in SDNP.
On a broader scale part of the reason Trailbiking is percieved as illegal activity is because we as a group don't celebrate the legal heritage of the lanes on a notable scale.
In france they have Randonee's - days/weeks when ALL users get out on the lanes and have activities to enjoy them.
TRF could organise similar, something of note and prominence that sticks two up to those attempting to demonise us and says look, were having great fun legally, responsibly and sustainably.
Said this for a while now and heard the counter arguments but I still maintain that the greatest threat to lanes is secrecy and lack of use.
We're the only user group that doesn't have a promoted national route!
No use waiting for authority to do it so we should do it ourselves.
Couple of events a year would be the best demo to counter the anti's.
A lowest to highest "randonee" - Littleport BOAT's to Grashills causeway
A coast to coast Kent to Devon (tried and tested

)
The routes to be advertised and promoted and made available to all so as to reinforce their legality.
I agree with you Jon. What you are suggesting is a "positive" way to go about it rather than what could be termed a "negative" way like blocking a road with bikes etc.
It is another good idea which largely goes unsupported by the TRF and would peta out if you did not keep at it .
Keep up the good work Jon. One day you will get the wider support. It people like you, Richard,AndyT and many others who make this organisation. It just needs someone to join them all up..........Oh yeah that,s what we have an executive for.