The diagnosis from the air conditioning specialist: He can recharge the existing AC unit on the roof of the trailer (which is producing less cold air than it used to do, although fortunately for us it's doing some cooling). However, the cost of doing so is likely to be roughly $500, compared to around $800 to buy a whole new unit (which would have the added benefit of not using a coolant that will be banned in a few years), and he can't guarantee that the recharged unit wouldn't leak the coolant away, since we can't identify where coolant is actually leaking. Alas, had we known this was coming, we probably would have bought one during our trip to Camping World in Wilsonville, Oregon after Westercon when we bought the new RV fridge; it would have saved us maybe $70 in sales tax. Lisa and I are discussing our options. She will probably stop by Camping World in Rocklin when she comes down to join me for the Westercon 66 open meeting planned for July 29 in Sacramento. If she finds a unit she likes, I might be able to stop by CW on my next trip home and collect it. It should fit into the back of my van. Lisa and I will have to install it, which will be a lot of work.
Unfortunately, this sort of thing delays further other planned repairs, since we need to keep at least one place habitable on the property, and living without AC of some sort in Fernley is a ticket to misery.