I actually set mine up last year, and it worked but I am planning on re doing it. Home Depot sells a white pre fab cabinet,actually like sectionals, there are a tad on the heavy side but confirgurations are limitless. A lot will depend on the number of bikes and trailer size, as well as what you want to use it for.
Mine I use to sleep in so I unobstructive floor space as well. [beats a tent]
To bench or not to bench..........what will it be used for, will you do repairs in your trailer that will require a bench or will cabinet/shelf space be more useful?
A life size diagram maybe helpful, use chalk on the drive way and draw it out. Include bikes and tools in the diagram or just use the real things themselves.
KX727 has a good Idea of putting the toolbox within the bench, instead of on top,