I honestly think the Park is overpriced unless there is some redevelopment value not being considered.
With only 10 units occupied, and using a blended lot rent of 250 (Park owned home rent does not appraise) means you've got a high level Park valuation of 10 lots * 250 * 50 (multiplier 12 CAP near 50% expense ratio due to septic and low occupancy) is about 125K.
After that you sound like you have a large number of homes that need to be hauled off, or thrown into a dumpster which will cost about 2K per home or maybe you can have them given away as hunting cabin specials at no cost - this could be a big cost though so you need to account for it.
Maybe low water flow stuff will work, but you cannot control (or maybe you can in the rules) how tenants conserve water in their homes - and your goal should ultimately be to have tenants own their homes, so it is advisable that the number of homes hooked up to septic systems meet the maximum flow specifications of the systems. As you said there are too many hooked up today it makes me wonder if they were ever permitted, which your city or county should have record of...and if they're not permitted and illegal expect to pay a lot of money to fix that issue.
Since two banks have been burned on this Park I doubt you would be able to easily get financing on it unless you're personally guaranteeing it - and even then they may not, it might be a cash only deal for you. Unless you have turned around Parks like this before the banks won't want to touch this hot potato.
Also keep in mind that even with the 10 occupied units there is a good chance half of them are felons, sex offenders, and have issues that would be unacceptable to run a respectable Park. You will likely have to evict people before you can get the safety, pride of ownership, and other building blocks in place to get the needed momentum to turn it around.
After backing out of enough transactions I have come to the conclusion some Parks are not worth turning around, and may even be easier to build from the ground up. You don't want either of those deals, and this sounds like it may be one of them unless you can get the price way down and can commit the time to get it handled.