My uncle is also a woodworker. He was given a nice finished workbench from a friend and he put it in his outdoor workshop which is not temperature controlled. We live near each other so the seasonal temperatures as virtually the same for us. Once a year had passed the bench was pulling itself apart, the ends of bench showed the most warping. From what I can tell it was laminated properly. It makes me wonder though....
I suspect that's as much to do with the way the bench he was given was made (regardless of whether it was commercial or shop-built) than a sign that a benchtop made in that way can't withstand wide swings in conditions*.
That bench was likely made at least somewhat like furniture, if not in exactly the same way. So the wood would have been quite dry and in damper conditions dry wood of course swells quite a bit. And because a workbench is not intended to be exposed to water they could well have used a non-waterproof glue, although it is possible the glue used is waterproof as they might use it for everything regardless (again true for both commercial and shop-built). If the glue used is a water-resistant or waterproof variety then it signifies that whoever made it needs to overhaul their glueing processes! Because well-glued long-grain joints can't come apart — the wood has to fail for a split to occur.
Long, boring TL;DR here about wood selection for maximum stability in a top made up this way but brief version, most tops are also not made from carefully-selected wood. This is most especially true of commercial glue-ups, where due to manufacturing expediences 99% of the time no consideration whatsoever is given to grain orientation from board to board. They basically grab the next board from the supply at hand and put it in there, regardless of whether its grain might put stress on the overall structure.
I suppose I could use hardware to reinforce the lamination but wood would likely still warp. I can accept a little warping but I don't want there to be room to put my fingers between the boards.
There are a couple of workbench plans that utilise the same method used in some butcher block construction, with through bolts (threaded rod). This could go a long way towards ensuring great stiffness and resistance to warping in a glued-up top, but it is a hassle in terms of construction because every board has to be accurately drilled multiple times before glue-up. Note: if you want to consider this it's worth pricing the rod right now to help make the decision as it may be surprisingly expensive, it is here, and you need four or more lengths of it the full width of your proposed top.
*I would personally ditch the idea of the glued-up top. It's not necessary for a functional bench and by putting it aside you can save yourself a lot of time and effort in construction, while simultaneously ensuring your top will be far less subject to movement with wide swings in humidity.
While I wouldn't exactly recommend the material I have seen a workbench in an unheated, uninsulated, draughty garage with an OSB top and as far as I can tell from just looking at it it hasn't warped in the 20 or 30 years since it was built. I haven't worked on it so I can't say how much if any movement has occurred but it certainly looked flat enough.
As you know board materials in general are far less subject to seasonal movement, so a top made from MDF, plywood, chipboard/particleboard or yes, even OSB, is going to be far more stable than almost any bench made from solid wood. With the added advantage that they're far easier and faster to put together (less than an hour and done is possible) and furthermore will often cost substantially less, which is nice.
