No, there are no pictures of the underside -- all the pictures I know of are here:
Schlor Pillbug pictures by NeilBlanchard - Photobucket
Yes, wheel strakes would help a lot. From the wind tunnel tuft test picture you can see the main problem area: from just ahead of the rear wheels and behind them, the air is swirling up. The tail may need to be broadened and flattened, to improve things?
The other main issue with the Schlörwagen is the width: it is 2.1m (6'-11")which is very wide, indeed. They made it wide so that the front wheels could be fully enclosed, even when they are turned fully. I think that some system of articulated/moving enclosures would keep the advantage, while greatly improving the CdA.