I did my avatar for FiberglassRV by drawing (probably in MS Paint - it was long ago) over a photo of my trailer (which was a Boler, but the method would be the same).
Software to reduce a photograph to something looking like line art should be available on all common computer platforms, but in most cases - at least among free or cheap software products - my guess is that you will likely need to trace the outline by hand, rather than getting a clean line from the software.
Assuming you have a suitable photo (any from the Escape Trailer website could be used), you can try this free of charge and without installing software:
RapidResizer:
Free Picture Stencil Maker