Bob, DynaJets and grass fields don't mix well. Especially if the grass is dry! The other consideration is takeoff. Unless they have been improved since I used to do it, DynaJets require a very smooth surface to get airborne, for a couple of reasons.
First, fuel draw is marginal, and any interruption or inconsistency will kill the engine. Second, most jet planes are oriented toward speed and/or training, and have very small wings for their weight. Wing loading is more like full-scale aviation, measured in lbs./sq. ft., and not in oz. This necessitates a long takeoff run to build flight speed, and any roughness (aside from engine-run problems) slows acceleration considerably. A grass field which would present no challenge at all for a PA craft could easily be totally impossible for a jet.
I'm not saying that it can't be done; virtually all problems yield to some combination of money, time, money, clever problem-solving, money . . . I am, however, suggesting that you're borrowing a bunch of extra difficulty in this task. Good luck.
Ralph