Is the acre of land all yours? Or will the other people be on it also? I don't think one acre is all that much. Put your trailer on it, room for parking a car, and you have to use all the rest for a garden. Are you planning on growing your own food? Or selling it?
Honestly, I don't think you are getting much of a deal, at all, with the acre of land. $400 a month, you have to pay for utility installation and then the cost of electricity, with no other facilities. Just for definition purposes, I wouldn't consider that "off grid". Who are you paying the $400 to? The "group"? Are you getting anything else in return? Help with the garden, watering, weeding, sharing of harvest?
The RV park you describe is $400 a month, utilities are already installed, you pay for electricity, and you have access to all the facilities on the property. RV Parks can be great places for kids to grow up at if you pick the right one, with playgrounds and tons of other kids to play with. You may well end up having "playgroups" with other families, basically sharing babysitting while your kid gets to play with similar aged kids. And you can always go help out at "The Farm" with growing gardens if you want, and (I would assume) get a portion of what is harvested.
Now... if the 1 acre plot was like $50 a month, then things are different.
I'm just going by the quick description of your situation and (a lot) of assuming. Hope all works out well!