I installed a door stop on both my previous 1300 and my current 4500. Bought a 6" plastic stop in cream, placed it directly under the 1" overhang from the top center level and just above the front running light
, horizontally, with a 3/4" cream painted block underneath it. The tricky part was aligning the bulb end of the arm and receiver at the appropriate place on the door, but after much opening/closing and eyeballing, happened to be just above the molded-in logo. Blue-taped it into place to hold until ready to permanently attach.
Then I drilled the four holes through the outside of the trailer (into the storage - it was about 5" below any seating and ensolite) and used a 3"x5" plate to disburse any pressure from pulling, then used stainless steel bolts and self-locking nuts to secure, butyl tape between all layers.
On the door, I didn't want to drill all the way through both sides of the door and didn't figure any sort of screw would hold up, so I had to use -- horror -- silicone! -- to attach the little 2"x3" holdback, again, blue-taping in place for a day until it set up. (BTW, this is the ONLY silicone on my trailer -- I'm a Lexapro girl where needed, but it doesn't have the "sticking" power of silicone.) It has held up for a couple years, not really noticeable as it folds and clips back underneath the overhang while travelling.
I'm sorry I can't attach a picture -- the trailer is about 25 miles north of me, but will do so when I get there this weekend.