Refrigerator Smell - Yuck!

Well clean it out every time after camping and leave the door open. some say leaving a cup of real ground coffee in the fridge will absorb some of the aquatic odour.

Cover the floor and any shelves it will stay on with coffee grounds.
After you do that for a month or so, if you are going to store it, put your bag of charcoal in there.

wash with Baking soda and water then leave a box of baking soda in the fridge
Good luck

Both doors propped open with dish towel and an opened box of baking soda in each. Reuse baking soda when you store the trailer.

Saturate a paper towel with vanilla extract put on plate or small bowl, and close door at least 24 hrs.
Neighbor does this with his coolers and I'm amazed.

You might try an Ozone Generator and direct it into the fridge-freezer.

Look on youtube. There is a procedure and instructions from Whirlpool.

You still got a spray bottle of bleach used for packages and bare-faced salesmen?
Spray everything inside should kill the source of odors.

I don't know how to get rid of the smell, but that seems to be covered already. What I can address is WHY it smells in the first place, and how to PREVENT it in the future. When in storage, make sure that the refrigerator door and freezer door are left OPEN. That lets air circulate in there and keeps the mildew that causes the smell from growing. In 15 years with RVs, I have never had a smell in the fridge or freezer unless I forgot to leave those doors open.

Small dish of Arm&Hammer. Wash in interior with vingar solution and let dry with door(s) open