not being able to put my hands on it makes it tough to give advice.
I am not big on fiberglass siding having any strength to use screw on, with out some nice size washers(fender washers).
I fixed a corner of an old camper(aluminum siding) by cut a piece of metal, slid it under the side trim and bent it to attach under the camper as well(several inches). I like that liquid nails adhesive to hold every thing together and then a few screws nicely placed. Many times your side trim has a plastic that covers the screw heads so putting a few extra there would never be seen. Paint and forget
If you can find something to push pressure(fence, house, bumper of truck and a board or two) against while the liquid nails dries you might not need many extra screws .
its camping, good luck
2011 Wildwood T26BHXL
2004 Yukon XL Denali
43yrs of camping; one lucky guy