I think plastic wrapping the luggage is a good idea and doesn’t necessarily send the message of the bag containing valuables.
If I’m not mistaken, each and every piece of luggage that goes on the plane is scanned/x-rayed for metals in search of firearms. Naturally the scanner will pick up harmless but desirable electronics and jewelry. If a person can reach in and pull these valuables out they will. The plastic prevents easy access and will not be sliced off as long as there is nothing inside that would prompt a search. In that case, TSA must inform you that your bag has been searched. I’ve had that notice on my luggage more than once, however nothing was ever taken.
My computer was actually a small netbook about the size of a 10” tablet. It could easily be concealed. Anything larger than that would be a challenge, but still possible.
Someone mentioned using ties which is also a good idea. If the ties are cut off, you will be notified. I use ties on side zippered pockets and ties PLUS a TSA approved lock on the main zipper. I take pictures of them before checking my bag. I also loop my luggage tags through the same zipper top as the ties. But bags that can be unzipped gives them easy access to anything small and valuable they spot when the luggage is scanned.
Fins should be safe, but if your gut tells you not to chance it, then don’t.