Good Morning Dingo Girl. It's been a while. You made it through another winter, although not as bad as some Michigan winters can be.
Those open A-frame channels under the coupler has always been a nemesis of mine. Mouse front door to my Airstream. I should put a little welcome mat out. I made little 5 by 1 1/2 aluminum "end caps" for mine and pressed them into the open channels. It helped. This area is also where rain water enters the frame rails and settles into the belly pan area while towing in a rain storm. Water scoops! The infamous rear bumper storage compartment and body to C channel seal is also a great place for a mouse to sneak in the "back door", as will as rain water to get into the belly pan area. (I call it my Airstream basement, and yes, it gets wet at times.)
There are so many mouse entry points in an old Airstream. I try to get them closed up, but I still get a mouse or two in my traps inside the Airstream. I'll bet the bottom of your trailer is as tight as a boat hull.
Your solution to the open A-frame channels is elegant! Hand crafted to fit perfectly.