here’s what I tell my customers when they say similar things:
tacoma beds are made of composite materials instead of a fully welded metal box. Composites do get weaken over time and CAN (not will, with 100% certainty) crack or even split.
Offroading and carrying heavy load introduces more stress to the truck, and can cause things to break faster or make things that are not supposed to fail… fail. That’s why if you wheel often it is a good idea to check your torques on nuts and bolts before and after each trip. That’s also why I change my tranny, t-case, front and rear diff oil way ahead of factory’s recommended intervals.
I’ve yet to see a loose suspension nut and bolt resulted from wheeling, but checking torque on nuts and bolts don’t take long and is good preventative measure. Changing tranny, t-case, and diff oil ahead is not entirely necessary, but it is cheaper to do preventative maintenance than to do a tranny, t-case, or diff. The fluids I dumped from my 4R at 40k miles from all the trailing and overlanding was way dirtier than one that spent its entire 60k on pavement just commuting.
Similarly, when it comes to bed stiffeners, they are just ~$200 parts that reduce the chance of something that MAY happen to 0. It’s cheap insurance compared to when the bed do crack/ split/ misalign and you have to get it replaced or fixed, even if the chance of it happening is next to none.
I don’t know about you, but when I build/ make/ plan things, I like to be prepared for that 1% chance of happening. That’s why we carry tools and spare parts on long trips and do preventative things: because when it comes to being on the trail, anything that could go wrong will go wrong at some point. Ultimately the choice is on the vehicle owner but it’s always better to be wearing a belt than be caught with pants down.
That’s just how I look at it. I can be scientifically proven wrong that taco beds will never split/ crack/ misalign in the future (ie: full on baja stress tested) and I’ll gladly accept that, but at this time this is how I see it: just a cheap insurance that makes sure it will never happen.