Assuming your driveway has a severe slope ( this most be so, if you are very
concerned)...why not just hook the boat to your rig; BACK the rig up the
driveway; leaving the boat and vehicle turned around? That way, the boat
will be pointing DOWN the driveway and won't be likely to slip off. Just
leave the rig attached while you make the change and then put the boat back
where-ever it is now.

I don't think my boat would slip off ( I have bunks, you may have rollers)
on a driveway without the lubrication from floating in the water.
--
RichG manager, Carolina Skiff Owners Group on MSN

http://groups.msn.com/CarolinaSkiffOwners