Hi Kieren, if you can rent a small SUV with roof rails - running longitudinally, you can get a couple of bits of timber about 120cm long, 2 x 1 pine or whatever and with some cheap thin rope lash the pine to the roof rails. The pine becomes your roof rails, then with a bit of padding and normal straps your are laughing. If they won't cut the pine in the hardware store the saw in a Swiss army knife will do it!
Hope that makes sense, roof rails run north south and rack east west like normal. And when you are done, just keep it all for next time.
Of course there is the old double beach towel rental car roof rack, roll up two beach towels to create a pad/spacer chuck the board on and straps through the open doors - the roof pops back out....well always has so far
Its really not as dodgy as it sounds and the board travels well. One little trick if you are worried about the board moving around, put it tail first, upside down, then you can use the leg rope attachment point to tie down to the front of the car. If you open the bonnet you can always find something to thread some thin rope through, for surfski's I put a loop of rope coming out on each side of the bonnet, if you are fussy a strip of duct tape on the edge of the bonnet to protect the paint. So when the bonnet is shut there is a little loop sticking out near the front of the bonnet on both sides. When the board is on the roof, just tie some rope through one loop, looped through the leg rope, rope (with a hitch to stop it sliding sideways) then down to the loop on the other side.
If you do that the straps through the car don't really need to be roof flexing tight, it will be rock solid even in side winds.
