How about drilling a few (4 or 6?) holes through the bed wall, closest to the cab. Use a few U-bolts + U-bolt plates - round-end towards the cab and threads pointed towards the bed.
You could either use a pipe to hold the flag pole or clamp the flag pole directly.
I suggest that you add some support (1/4" steel plates) to make the walls more ridged where the U-bolts go through the bed wall.
If you have any muffler U-bolt plates around, they would work great to fasten the pipe or flag pole better.

Hope that makes sense. I can draw it, scan it and post it if need be.

Hope that helps!

 

i didnt said it right i mean the tube is a base for slip the pole in. Just a base

 

Make this and bolt it in the bed http://www.google.com/m/search?site=...d+square#i=135

 

I can kind of picture it! thanks! i will definantly be thinkin of this idea when i head to home depot for u bolts.
this is actually better then what i was thinkin, bout the same concept but you got it a little better!
thanks

 

Cool! Glad I could help out.
Good luck with it. I hope you post a few picture when its all setup.

 

will definantly post pics! got the u bolts just now! drillin holes and puttin it together! goin to a bonfire tonight so ima be showin colors with pride out there! AMERICA!!!!