I have repaired them by drilling a shallow impression or two on the crack inside the forend and then using a plastic syringe to force clear epoxy into the crack. Try to get some epoxy in the full length of the crack if possible. Surgical tubing can be used to hold it together until it cures. You might want to use a block in the barrel channel when applying pressure with the surgical tubing. After the epoxy in the crack is completely cured build up a layer of epoxy on the inside to reinforce it.
ou.3200 - I have successfully used a system similar to yours. I open up the inside of the crack with a fine file and also cut a few cross channels to give additional strength. A small hole at the end of the crack is important. If the crack is in a pressure area, I used to use small metal inserts (made from small cut nails) as cross ties. I have now been convinced that bamboo cross ties are superior.
Most important, figure out what caused the crack. Often, a bit of inletting work is required before repairing the crack. The job is one that can be done with little effort at home.
It's highly likely that the wood is cracking because the 3200 forend iron needs to be updated. The forend iron has probably developed a crack, and now is allowing the wood to shift or the bending of the iron, causing pressure on the wood.
If it has not been updated, send it to Pat Laib, ASAP. Just repairing the wood will not work. Eventually, the forend wood will be destroyed.