Anyone have any experience making or using a trailer for a small (30 lb.) dog ?

I have already googled the idea and looked at all the pre made and ideas for home made trailers. Some of them are just a dog crate on a flat bed, or a frame. Very simple, and easy to make, but not cost effective.

I'm thinking a cheap way is just a kids trailer with some plywood & carpet on the bottom to prevent rips.