Recently I stumbled across this site of some friends at Rebbl, a Dutch conversion company with a special interest in Volkswagens. They have converted old VW Beetles, but also the transporter vans. Besides the VW line, they have also converted quite a few other brands as well, though the VW just appeal a little more to me.
Having build up a lot of experience from converting conventional cars to electric vehicles, they have opened up a part of their website to share their knowledge with the world and help you with your conversion. Besides the various books available around the web, they have opened up the Rebbl University to teach you the ropes of converting to an electric car!
These guys know what they are talking about and recently got their TUV approval for their conversions, a great achievement and it demonstrates the quality of their projects. Also note, I am not an affiliate for them, just a fan of what they do.