3" wheels or similar will help on larger planes, such as a 40 sized trainer, but not on this plane. If it is the min-Funtana I'm thinking of, it has a 30" something wing span an weights 1.5 pounds. 3" "standard" wheels will kill that plane. Way to heavy, will mess with the balance point and move it forward and down by a lot, add too much drag, and would look totally silly.

IMO, you best chance of getting a setup that will work in grass is to use pylon racing wheels like the following.

http://www2.towerhobbies.com/cgi-bin...?&I=LXK845&P=7

These are cheap, should bolt on with only a minor change (remove pants and maybe new bolts for axels), aren't very heavy, etc. Their thin section will allow them to roll thru grass with little resistance, and they are larger in diameter than the stock wheels.

If that doesn't work, you might try stripping the gear. That plane can easily be hand launched and belly landed. Doesn't look as nice in the air without the gear, and you may need to put a skid plate on the bottom, but it is better than tearing out the gear due to tall grass. It can also be harrier landed if you have the skills, which is almost a zero airspeed landing.