I'd look at good old fashioned carriage bolts. Use a forstner or Spade bit to countersink the hole before drilling the bolt hole. I like the idea of routing the edges, maybe a tounge & groove for the overlap to keep warpage down if you only use one bolt per point.
As for finish, maybe look at a deck stain to protect the wood? If you paint it too dark, any scratches/abuse will show up as bright white scars. just a thought anyway.

1956 GMC 370 dump " 'Tater "
1970 VW Volksrod "the Black Bomber"
2007 Chevy Avalanche
2020 Jeep Cherokee Trailhawk,
2005 Harley Davidson FLHTCUI

I dig all cars, old and new, whether they were hammered out of American iron, German steel, or Japanese tin cans. Being unable to appreciate them all is missing out on a world of great things.
But thats just MY opinion! :P