There is usually more than one way to skin a cat and fore end work on a Handi is no different. Excellent results have been done using different methods. Some times just an O-ring, some times RTV bedding, well, the imagination is the limit. I do some thing just a little different than most. First - I make sure the lock up is good, you will never get a Handi to shoot well until your lock up is good and tight. Second - When the action is open I like the fit to be loose, almost sloppy. It drives me nuts, but that is what seems to work. Third - I put a pillar in the fore end and epoxy it in with JB Weld. Look in the FAQ how I do it. You may have to adjust the fore end "slop" after the Pillar has set. Fourth - I bed the entire length of the fore end to the barrel with JB Weld. I can get pretty good accuracy and can rest the fore end on the bags or use a bi-pod in the typical location. I have not worked with plastic fore ends, but you could adjust the slop by plugging the screw hole with JB Weld (BTW I really like JB Weld if you can't tell) and re-drilling the screw hole a little closer to the action, you could put a pillar in while you are at it.
Good Luck and Good Shooting