Ive always pictured building a bridge out of the light trailer house frame Ibeams, you can cut the center struts and lap them over each other and make it pretty narrow, also if a person was real artistic you can cut a small v in the bottom of them in a couple places and bring that together and weld it creating an arched walkway, for possibly very little out of pocket expense, they will almost give you the trailer frames to get rid of them. obviously this is an easier project for someone with a welding and fabricating skills.