http://kaadengineering.com/powermover/
I highly recommend Brady at Kaad. I have an AC8 that moves an 8,000 lb boat. It's great. In California, I save about $2,500/year on storage costs plus I have the convenience of keeping the boat in the garage.
In any event, I've found most of the objections to trailer dollies are FUD. I read all the negatives before I moved forward, but, frankly, most are minor issues.
Brady will listen to your requirements in detail and then add custom features to the dolly as needed. Mine has an on/off switch for the brakes (no need for a controller...just need to send 12v+ to the brakes) that I use quite a bit since my driveway is sloped up. It's powered by 120v and I've never found the 50' cord to be an issue, but I'm not moving mine very far..
He typically does not use the trailer's hitch--rather, he wants you to attach a bracket further back from the tongue. This puts more weight on the dolly and gives you more traction. Plus the attachment is very stable.
