Great work mate! Really like the use of classic joinery methods - have ofthen thought about this as we try to use as much materials from the site as possible but it is somewhat counter that logic to use metal nails. You have any ideas for anti skid treatment for the top surface?
not sure how common it is, but I theorise Bed Liner type paint(for the bed of pick-up-trucks) would add some grip (applied with stencils) I am also trying to come across an old grooving plane to maybe serrate the surface, the bridge will likely only be ridden in dry conditions, with a section of the bridge folded up and locked when not in use (rodent problem)
Could be an idea but I would think the results depend a bit on how permeable the pain is - you might as well end up encapsulating moisture and get rotting directly beneath the pain layer. Grooving plane sounds much more in line with your overall approach & would probably make for a nice wear of the bed surface over time.