One thing to consider is the scamp
aluminum belly band is cosmetic, not a seal. At least from having mine off and what others have said. It just hides the lip where the top and bottom come together, the seal is fiberglass on the inside wall.
This makes me think that small holes the size of the rivet holes would be a possible attachment method.
You might want to check at an Ace hardware store for some aluminum angle about 1/8 thick x 5/8 x 5/8 judging from my scamp
. Or maybe 1/16 thick.
Cut pieces of the angle off maybe 1/2 inch wide (or so) this will give you little aluminum "L" shaped pieces. Drill a hole on one leg of the "L" and round the corners of the other leg down with a file, grinder etc. and you can rivet to the belly band through the hole.
This would provide a little rounded "tab" sticking up on the outer edge of your belly band to keep your rope lights in. You would just drop the rope behind the tabs.
Since I can't draw it. Try to picture it below as a cross section with the L shaped tab on top of belly band. With a rivet going down through the bottom of the " L". The = sign represents the two FG lips of top and bottom of camper shell they typically reach most of the way to the outside of the belly bandl.
Not to scale.
Not sure what size rivet it would take, belly band on mine I used a variable 1/2 - 5/8 rivet. You would probably need a bit longer to handle thickness of the tab. You need to drill through the top aluminum and the two FG lips but not the bottom of the belly band. Just rivet in the same line they did, don't think you would need very many tabs, you probably have an idea of what it takes from how many binder clips it took.
I suggest Ace because they can order many sizes of aluminum stock if they don't have it in store.