Well Chris it would be easier to modify a kit than an ARF. The 2 support ribs in the wing for the servo bay that will hold the servos can be replaced with harder wood during the contruction process, but an ARF's balsa rib can be built up also by using the sandwich method and have harder wood installed next to the balsa rib in the middle. Glue the harder wood in making sure it touches the spar, sheer web and trailing edge. Bass wood can be used to make the hatch and hatch support rails on the inside of the ribs for the hatch to screw into. This will add a little weight, but shouldn't be to much. If you build a kit, this could be done during the contruction. The covering on the ARF will have to be cut to get into the wing. I would recommend installing a hatch up front underneath the plane also, to allow access to the fuel tank and battery placement. This would be a great benefit once you haved finished and trying to balance the plane. The turtle deck can be sheeted also if you want to. This is the only part of the plane that is very weak to me. It is not a neccessary addition, but if you do not sheet it, you have to be careful with this section of the plane if it is not sheeted. Mine is not sheeted, but it would help on stiffing this section up.

Remember Chris, I built a 4*60 which may be a little different in contruction from the 4*40's wing. I haven't seen the inside of the 4*40 wing.

I used my $20 digital camera to show you some illustrations, so over look the photo quality... LOL