Sharon its thin on that side due to how tight the door often is on the hinge side. I assumed it was due to years of compression on mine but as yours is fairly new perhaps they shave down that backing or something at the factory to accommodate for the that.
The problem you are having with it wanting to slip off is also due to how tight the fit is on that side and why the foam gasket Scamp
installs often slip over on that side as well.
I have tried this mod with two different sized gaskets now and have not been able to get the door to closed unless someone is on the outside and pushing hard while I pull it tight on the inside. :-((( I camp on my own often so not always going to have someone to push on from the outside to shut it for me and I am not sure that when I do have someone with me they would be to pleased to know that after they help me close the door they have to sleep outside.
I know some others who have done this mode have reported that they have had some difficulties with closing the door after doing this mode as well, but I am thinking that perhaps my door just fits tighter than some others. I have given up on this mode for this year as it was getting costly ordering different gaskets to try. I ended up ordering new foam gaskets from Scamp
so I could go camping and not worry about not having any gaskets on the door if it rained. A bit disappointed due to having spent hours cleaning up around the door frame after getting rid of the old foam gaskets. Actually took a chance and went to NOG for 5 days without any gaskets, as I was waiting for my second order of attempting to find the correct sized rubber gaskets to arrive. Happy the weather was good :-)
What I have learned so far from attempting to do this mode is that the foam that Scamp
uses around the door is only 1/2" thick and it easily compresses. Some of the links and photos of the gaskets that have been posted here are much thicker in total than that and they do not compress as easily. For this mode to work well on all Scamps I suspect that one needs to find a gasket that is no more than a total of 1/2" in thickness and made with fairly soft rubber to allow for good compression.