Ameyam, another idea for you.
I just had one of the nuts in the wing fall out and had to drill a hole per rickstubbz instructions in 2009.
attached picture will show what I did. I made the hole 5/8" diameter because that was just enough to get my finger in there to push the plastic T-nut back into place.
You can feel the plastic T-nut better on the rear wing mounting hole to understand its size and shape. The T-nut is 25 x 12mm on the back, so you can drill a hole whose edge is as close as 13mm from the bolt hole centerline without hitting the T-nut. If you drill a large enough hole, you should be able to coat the OUTSIDE of the cardboard tube with thin CA a few times and harden it up.
Of course, this is easier on the back side of the tube, where there is already a large hole that lets the wing servo wire run out. I would suggest that you do both front and rear of the tube with thin CA to strengthen it for that heavier engine that you are using.... and keep your landings gentle!

I am attaching a photo of my two wing roots so that you can see the hole that I added. My hole was smaller and further forward that you would want for access to the forward side of the tube.
My goal was to get far enough away from the wing tube that my finger would fit for manipulating the T-nut back into place. The material there is two layers totalling 5mm, one 2.5mm layer of the harder plywood that we see on the outside, then another 2.5mm layer of balsa on the inside, so don't push too hard on the drill or knife after the first 2mm.

And don't forget to check that your wing tube isn't too long. Mine was. Both wings should slide right up tight to the fuselage at the same time without the bolts. If they don't, you are stressing both the wing and the fuselage sides for no reason or gain.

EDIT: here is a link to the Post #956 that Rickstubbz did back in '09 with a much bigger hole 7/8" = 22mm:
http://www.rcuniverse.com/forum/m_47...39/key_/tm.htm

If you move that hole so that its closest edge is 15mm from the T-nut/wing bolt mounting centerline, you should be fine up to ~Ø25mm and have plenty of access to see the front of the tube for CA hardening the tube, and maybe even add a little epoxy where the tube meets the spars. If you have 30 Minute epoxy, maybe just use that for everything, coating the tube and attaching it to the wing spars. 30 minute epoxy is thinner, and slower drying, so it will soak into the cardboard better than 5 or 15 minute versions.