Hello Fabrizio,
I've been on the same quest and finally decided to have one made by Backstage Equip. Inc. They had a prototype I had seen that fit what I wanted and I was able to get them to make some modifications for me that made it perfect. They call it the Shot-Saver Dolly. It's small and extremely versatile only 3 ft. long, you can ride mounted to it or use the standing platform and step off. The dolly's frame widens and contracts to get through doorways or widens for more stability.The wheel base can also be shortened or lengthened by moving the front wheels forward or backward on the frame. Wheels are easily interchangeable, to start I got 16" frontwheels and back wheels are two 8" double caster steering wheels that have tension adjustments to take out any wabble. They also have 20" wheels and ballon tires for the beach.
One of my main requirements was that it be easily broken down to a shippable size. I was able to take it apart and fit everything, including wheels and seat into a Tough-Bin trunk size case so I can always have it with me or ship it.
The price started at $3,200. I had the tires filled with foam, so no flats, that was extra. I don't have any pictures yet but Backstage might.If your interested contact Sig at Backstage (818)504-6026.
I'm really happy and can't wait to put it to use!
Cheers,
Randy Nolen