John,
I had a similar (albeit smaller) situation on my hands when I bought my first park 3 years ago. 6 homes, all rented when I bought it, and all vacant a month later due to issues similar to what you described. I too had the decision to remodel or replace as they were all in rough shape. I opted to remodel 4 of them, and demolish 2. As it turns out, I should have remodeled 3 of them and demolished 3. I am a contractor, know what I'm doing, and did a lot of the work myself.
Whatever you do, make sure you don't bring new trailers, or spend so much on remodels that you price yourself out of your rental market. I have the most expensive trailers in my area averaging about $475/month including lot rent and no utilities. I can get this rent because I did a nice job remodeling and I now have the nicest trailers in the area. I have people wanting to move in all the time so vacancy is never an issue.
When it was all said and done, and what I'm moving forward with on my next larger park that I close on in two weeks, if I have to spend much more than about $6,000 on the remodel; I'm selling/demolishing and bringing in a new trailer. In my area, I can find a newer, nicer trailer (takes some looking around and negotiating) for about the same money. $4,500 +/- to move it in, put new decks/stairs on it, replace flooring, paint, and misc repairs. I'm in it $10-12k, and can rent it all day for $475 a month. I have also sold 2 of them, but since I did the repairs, and now know how their built, I have very little maintenance.
The one remodel I did, that I'm in about $12k, I would never do again. Its still an old trailer; lipstick on a pig.
I found a local guy that did the demo/removals for nothing. He is a Scrapper and he saved the old flooring, HVAC units, toilets, steel frames, etc. We both won. It took a couple of months for him to get rid of the trailers, but that was fine with me. (We split the dumpster fees for the unusable stuff, about $300/trailer.)
2 year pay-out, happy tenants, low turnover, low maintenance, high demand. Town LOVES me because I turned a dump into a nice little family park.
I would be happy to discuss more with you if you like.