How to preserve papalo

I think freezing would be your best bet - not fantastic for the texture, but when defrosted you could make a pie/cobbler or other cooked item with them. Plenty of web sites (eg http://www.fruitexpert.co.uk/using-up-a-plum-glut.html) say you can just halve them and freeze them on open tray, then when they're frozen move them into plastic bags. It's the lowest-effort option so probably worth trying on at least a fraction of your harvest.

Vinegar and sugar make good preservatives. Provided you use sterilised containers - place them in boiling water for twenty minutes, add the sauce, seal, then boil again for ten minutes - you should be fine. Store the bottles/jars in a cool place out of direct sunlight.

Avoid using oil during preparation, as you run the risk of introducing Botulinium into the mix. This would probably be neutralised by the vinegar, but it really isn't worth the risk.

As always, if the sauce smells or looks suspect when you come to use it, throw it out. Again, it's not worth the risk of food poisoning.