Fitting them is fiddly as long pop rivits are used & to get the right look the rivits need to go into countersunk holes so they can be filled before (yes) covering everything with yacht type varnish.
This is the original look and does look very smart.. however, there are downsides, as with everything, so its a compromise...
Holes in the load bed - and with time, water ingress into the locker compartment. I've since welded all mine up and now have a dry locker, after a few years its likely water will get in with rivetted slats, although I like the suggestion of using a silicone sealant like RTV under them
If ally rivets are used, and getting steel pops these days requires ordering them usually... With ally into steel in the longer term, there's the chance of bi-metaliic corrosion, though the aircraft industry has long used this stuff between dissimilar metals, or metal and wood... can still get it fairly easily.
Duralac assembly compound
I imagine these days, the right silicone sealnt would be a good substitute, other than for metallic stres-bearing assmeblies e.g. the rear wheel hub to radius arm joint where a chromat paste liek Duralac is ideal.
Having to load up and shovel anything from a truck load of wood-chips to horse manure from time to time, and recently a ton of decorative garden slate hippings, a smooth load-bed is imperative. Lining it out with a quality plywood (marine ply, or the next quality down) is ideal, and even using same to build up the sides as tree 'surgeons' ? do, tapered from the cab downwards, is fairly easy with timber. Treat it with a micro-porous wood preservative after ripping down to size... a good place for the join is just in front of the engine hatch, so two pieces butt perfectly and don't need fastening down.
Others use chequer-plate ally, 3/16" is about the right thickness, fitted noce and tight, hopefully with countersunks around the engine hatch if intending to shovel loads on and off.. though chequer plate catches the shovel unlike ply (ply all over is also a good sound deadener).
If the load-bed is already 'well gone' then quite a few remove the whole thing, a lot of work, and re-lay the new surface on the framework below.
There are also custom spray on load-bed liners, plasticised or rubberised layers, but they're not cheap.
.... so bear in mind what you want first, a smart original looking councours finish, a load-bed for sliding smooth solid loads onto, or a more workmanlike, robust and durable smooth finish for loose materials.
