I have a combination of pull outs in my Tundra Long Bed but the handiest by far is when I replaced the side windows
in the shell with Windoors.
On mine they were an easy direct replacement for the windows
that were standard in the shell.
Worth looking into for sure.
With the Windoors I can reach almost all the way across from one side to the other at least to grab or push or pull things out or across the bed.
The Packrat are pretty pricey if you buy them new or used and they can also be heavy but I do have several of them and even some extras if you were near me that I might sell cheap,they are just taking space in storage right now.
What I have that works the best though are long sliding drawers that just slide on metal rails with no slide mechanism at all.
Mine are 6' long and loaded with stuff they still slide well enough to be useful to me.
Not sure when I can but I will try to get a pic to give you the idea.
Buying full extension slides and making a box will clearly be the thriftiest method and should work well depending on your ability to build things?