I have the bed back on my 48 and put on the fenders just to fit everything. The fender gap was alittle off not to bad. I can adjust it out. My brother in law took a tape and measured from one corner to the other and there was 1" difference between the two sides. He said I needed to square it. Not quite sure how to square a truck bed or if it is even that important. I've had alot of trucks old and newer and never heard of squaring a bed.So should I square it or will it matter? If so how do you square a bed? Sorry for the long post.
Thanks
ART

 

If your bed is not square it will look like your truck is running side-ways down the road, if it is out of square it means that it is diamond shaped, say one front corner is ahead or behind the other, to square the bed take a regular carpenters square and hold inside the front corner of your bed so the short end of it is against the front panel of the bed with the long end along the side of the bed, the 90 degree angle of the square should rest flush on both the front panel and the bed side if it is square, if not shift the bed back or frontwards until it is square, Garry

 

You can use Garry's method..that will work,..But your brother inlaw is right also..

I'm not real sure what you have there,but I'll throw this at you..see if it makes sense to you.
Open the tailgate(if it is even on),stand at the back of the bed on the drivers side..using the tape measure,extend it inside the bed,..across to the 'passenger-side' joint where the bedfront panel and the side panel meet ,back to you at a point where the 'driversside bedside-panel'and rear bed crossmember' meet. Try making this measurement where the bed floor would be.Do the exact same thing from the passenger side,..and compare the dimensions...they should be the same if it's square.,if it's not then it's not square..but a diamond shape as Garry says..Push or pull one side or the other in small increments untill the #'s match...It's a 'diagonal thing'..take care that the tape measure'end' is in the same place in both corners, and that you read the final result from the same point at each end for an accurate measurement.
You can practice this procedure on any 'known' square.Sometimes using c-clamps helps hold things in place..( the bed-sides) .I like using the c-clamp visegrips myself. Once the bed is square..be sure and crawl under the bed,reach up and measure the distance from the bed-side to the frame ..front and back , and make sure your measurements are the same,..side to side,.. now the bed is 'square and centered on the frame'.
Hope this helps!

 

Thanks for the info.I'll go out tonight and see if I can get it squared up.
ART

 

An inch difference in the diagnal measurements is only about 1 degree of angle. This might be close enough to square to fool the eye and it would be hard to correct with a carpenters' square. I think that adjusting it using the diagnal measurements is the best way.