I assume you are talking about wind loads? I'm not really sure this is something he is worried about.
He could leave a truck parked on those ramps, that might hold it down. Or he could raise those flat solar panels up a bit and put a bunch of cinder blocks under there. Drive some ground screws in and tether it down using a handheld auger? Put legs on the back so when the wind starts blowing it over it hits the legs first and has more resistance / support? Obviously it's not to code, but if it's on his huge yard and he wants to do it, more power to him.. get it, more power? ?
Personally, I think he should do them up like a teepee Ʌ with panels facing E/W touching each other at the top at an angle, and load the middle with secured cinder blocks. If wind manages to come and take it away, he would probably have bigger problems than his solar trailer.