What Rollin said about height. I have converted a 18' 1957 Silver Streak before, pretty much the same thing as what you are working with. Unless your a hobbit a roll up on the inside will make it really short.
Your best bet is finding someone experienced in metal fabrication and having them use the existing panel, reinforcing it, and putting prop shocks on it. That way you will have a really nice awning to keep the rain out as well as a service window. From there, measure out the height of your deli case and install a sliding window above that height so you have a screened and sliding window on top, deli case on the bottom, nice cover to keep things safe and keep the rain off.
Find someone who knows what they are doing, once you cut you can't put it back without it looking like crap.
If you want, email me at alice.mckenna1 at gmail dot com. Will send you over some inspiration.
post edited by a.mckenna - 2013/02/16 11:25:53