The thing about all the modern replacements is they all are not cheap either. All will require door modification, cutting additional holes and sometimes patching fiberglass.
Meanwhile, vintage replacements can be found. These original locks lasted over forty years. If I can get twenty years out of a replacement, that will outlast me. The "trick" is to not jump on the first one you see, some are grossly overpriced.
I see nothing wrong with the Bargman L400 design. But after so many decades, stuff wears out. OK, I do see one problem. The shape of the L400 is unique, so replacements are not plug and play. Maybe, just maybe, someone will reproduce this lock, but maybe the market is too small.
Note on perhaps the BEST replacement option above, the Boler
kit. From the seller: "This lock kit will not fit fibreglass trailers that have a moulded profile around the door lock like Trillium
.... the lock will not work on doors thicker than 1Ĺ” So how thick your door is, and how flat the surrounding profile is, will determine if this kit works for you.