Sanding the inside of the box- input needed

[Coley]

Ok guys
I am getting ready to get my truck in for some updated paint....not show stuff but reasonably nice 'driver' quality stuff.

I am going to get the shop to spray the inside of the bed as well, but they said I would be well served to give it a quick 'sand' prior to them priming and painting it.
I started by giving the inside of the box a very, very thorough washing and de-greasing, etc....so that is largely done.

Now....
So...what is the best way to go about this?....180 grit? or what kind of quick sanding element? some type of brillo pad? or?
Orbital sander?....quick hand sand or?

Remember.....this is not going to be either show quality paint or show quality budget stuff, that is simply not in the cards.

The truck will be 'back in action' this spring summer with boxes in the back or the odd 2x4 or taking a few things to recycle etc.
It is a nice, light duty 'town truck' for me and my seasonal driver so I have no need, no requirement and no interest for show quality stuff....it simply isn't a good fit at this point in time.

Many Thanks!
Coley