Semi-beginner with some questions...
The thing with the Lipo's is matching them to a motor. 2 1020 cells at 7.4 v will put about 4 amps out, half of what the stock motor will draw. So you then need to go to a 2 series cells in parallel (2s2p). You will end up with 7.4v and a whopping 2000+ mAh, and the ability to pump the desired 7-8 amps. Your flight time will be well over 30 minutes, but you cant do like the Nicads and recharge in 15 min. So you make more $40 packs if you wish more time. the one pack may be plenty. The weight will be about 3 oz, which is stunning for the capacity! Lipos are the way to go, if the $ can be spent.
As for the tube, yes, shove it the whole length. It gives the tube nowhere to go in compression, relatively. High speed auger flights will do it in, but the little wind driven cartwheel or stall-boink will not screw it up. Stock, it can take quite a bit of abuse, but it WILL slowly bend there eventually. Very easy mod, sand it enough to pass with mild friction, not too much that you cant get it passed through. No glue, just friction.
By packing tape doublers I meant applying tape to reinforce where they stab and fin attach to the fuselage. You normally just stick the foam to the metal with double sided tape, then use the white long square thing that functions like a washer for the 2 screws used to attach the foam. When this is done, the weak point then becomes the line where the doubler & fuselage end, the point where the fin is all foam beyond the sandwich made by the plastic piece. If you add tape to both sides of the foam itself, you gain str right where it was the weakest.
Another thing to do is use epoxy on the fiberglass leading edge rods, not just tape alone. The tape is good because it spreads the load out over more area, instead of making the epoxy-foam edge the weak point.
Move the control horn in on the rudder and elevator to increase the throw. Really wild throw is fun on the stick, really tight loops are possible, like 4 foot.