Do they have to be portable?
I have been tasked to build lifting platforms for my units HITT Locker (basically a shipping container full of gym equipment with squat racks attached to the outside). The container and therefore the platforms I build will be outside in the Eastern North Carolina weather (hot humid and rainy). Any ideas on how to weather proof the platforms to make them resistant to the elements? Bonus points for longevity.
Do they have to be portable?
Ummm, horse stall mats stand up to horse urine all day, so I think the mats will do OK. If you're talking about a dead lifting platform you could just pour concrete instead of the plywood and then use horse stall mats under the plates.
That would be idea but it is not a requirement I was given.
There is already concert out there...but its not level the barbells tend to roll all over the place.
I used treated plywood and coated it with Thompson's with mats on top, set on brick pavers. You can also use a few coats of oil paint if you really want to protect the wood. I think it should last a couple years. I'm in Miami, so hot and wet.
This. You mentioned the existing concrete is sloped. Just level it up, throw some stall mats down and I would highly recommend adding a roof. A simple sheet metal roof with enough overhang to keep the area in the shade most of the day would do the trick. Connect one side to the container and set a post at the other corners. Metal sitting out in the sun gets extremely hot real fast.