You are always going to have this problem even with larger bolts unless the holes are reamed and a very close fit to the bolts. ie Sholder bolts. It will be to a lesser degree because you'll have more torque with larger bolts but still it could move. Epoxy will help but only upto a point, it certainly won't hurt until you come to take it apart again or decide to weld it up, then it will be a bitch to get off.!!

Don't you know anyone with a welder.? it will take 20Mins max to weld those few pieces together and it will be so much stronger. Forever.!!