Ricardo,

I use 30 min epoxy. Sometines I thin the epoxy with alcohol and mix in some microbaloon. I only thin maybe 20% because I want full strength.

Before I install the wing or stab tubes, I insert a small wooden dowel and measure where the inside half rib is. There are two of them. Attached is a photo of the rib location dimensions. You can tell because the wood dowel catch the support hole for the tube. Just mark the location of the half ribs on the outside of the wing. Then you insert the tubes and measure where they insert. I insert the tubes until the foam in the wing or stab does not allow the tube to be inserted further.

Inorder to keep epoxy from getting inside of the tube during insertion, I install with CA an 1/8" thick balsa plug at the end of the tube.

Then I use a inexpensive acid brush with the bristles bent a little to smear epoxy at the half rib holes. I also smear epoxy on the tube at the support locations. You do not need epoxy on the foam hole, just at the ribs. Using a twisting motion, simply insert the tube sockets to the proper location.

I think you can see the tube socket plug at one end.