Folding boat trailers

Hi all , I was hoping that someone out in cyber 4x4 land could afford some advice on these folding boat trailers as I was away at southwest rocks early last month and almost everyone that had a roof top tinnie had a folding trailer on there caravan I hardly got to use my little tinnie with my 2 boys due to the fact that my wife struggled to help get the boat on and off the roof ( she is not to blame ) and I saw that a fellow had a brand called little bull dog it was great but a little to much in the coin department ,I saw a few brands but was most Impressed with a home made unit which is something I'm thinking about, my worry is will the authorities rego the thing once finished or am I wasting my time ?? this was very simple a 40x40 draw bar that folds in half ,a 40x40 RHS axle with a 300mm length that accepts the draw bar welded in the centre bolt on guards and little 10 or 12" wheels with stub axle that slips into 40x40 RHS this is only going to be towed at low speed for a few K ms at most , I hope I can get some useful advise from you guys as I want to make this before easter !! so wish me luck.

Regards J,B.