Here's how I have always mounted my finished T-bolt heads.
I used material skids from work that I reinforced with some 2x4s.
The skids are really nothing more than 2 2x4s about 2 feet apart and
a little longer than the horn. Notice the position of the horns in the pics.
I've run the rotators for extended periods on these skids and they don't
tip over. Yeah, I can grab the horns and tip them but I just let them run and
the 5 I have built-up like this were all stable enough to run the rotators.
Here's sort of an explaination photo. Don't know if you can read it.
The main thing is to get the rotator plate bolted to thick pieces like 2x4s or
2x6s screwed to the skid. I used large wood screws while assembling my
skids.