They were everywhere but I never see any now. They'd be steel, originally painted white, rounded lid/lids at the sides, and either two flip up from the side (gullwing) or one big hinged at the front. I liked the ones made by the utility body companies like Reading with paddle handles to open. Hiway Products makes the closest thing you can buy new that is pretty much the same as ones made back in the day. I think they are all aluminum now, but you can blast and paint or powder coat. I searched steel pickup saddle box and came up with a picture of this blue one. And it looks like it's steel. But when I went to the website listed with the picture this one didn't show
I did go to 800toolbox.com and saw aluminum ones that style, but not that exact one. I like that blue one. I used to paint mine body color.
How about these accessory wheelcovers? They are Western Auto or something like that. I have these for sale over on the parts board (not here). N.O.S. mint condition