Hello tjotter,
Some things to consider;
Aluminium and galvanised steel react very strongly, you may want to insulate the walkway from the trailer.
I made my walkway out of a plank of treated timber, very cheap, held in place with zip ties, no corrosion, no drilling holes in the trailer, has worked very well for a few years now.
The plank came with a grooved finish = non-skid.
Some one else may have even better ideas.