I went bought two different electric trailer movers ( $2500 ) & they did not work on my grass moving my 17-foot camper. I finally called the company and they told me none of them work on grass or gravel.
Then I came across moving trailers with a front hitch. For $350 total I had one installed on my Chevy Colorado. It is AWESOME! Here is a YouTube video of me moving my trailer to the backyard.