So ... switch to electric trimmers. They will love and and you will get the bid. Put solar pannels on the south side of your trailer to recharge the batts. (Mostly for show) as you will probably need to charge the many batts and spares in the usual way, every night. And if you can use a propane powered clean burning mower or two--so much the better
Otherwise, of course, four cycle trimmers burn a lot cleaner than smoky two cycle.
Otherwise, its mostly a function of the gas you use. A gallon of gas produces a certain amount of carbon dioxide...the less gas you use the better. Diesel slightly more efficient.