A coupple of things come to mind, that you may have thought of already:

1. make sure whatever you build, it doesn't trap any water

2. make sure that, by strenghtening that particular section of the frame, (whatever you end up doing..), that you aren't just moving your weak point further under the truck. In otherwords, if you did hit this bumper hard (or pull really heavy), you would WANT the damage to your vehicle to take place out at the tip of the bumper.. where you can fix it. -just like it did the first time! :-)