You can buy 12V versions of a powered jockey wheel for under $300 on the Bay of Fleas just now; http://www.ebay.com.au/itm/Motorize...Power-Mover-Dolly-350W-Top-/252735087413

A google for 'powered boat dolly' then selecting 'images' brings up plenty of examples, too.

My brother has a ski boat, so he snaffled the old man's Greenfield Tractor ride-on, when the old boy gave up mowing lawns. Fabbed a towball mount for the front of it, and uses that to manoeuvre the boat trailer [it lives in the garage - the cars got a carport]! He's got a pop-top caravan now too, so it would get used for moving that as well.

Cheers,
Gadge

"ODK Mods can explain it to you, but they can't understand it for you..."

"Crazy can be medicated, ignorance can be educated - but there is no cure for stupid..."