Asphalt and concrete are really really expensive. Given the POH situation I would make this a secondary consideration. I don't think it's a reason to not do a deal, just take care of the roads and consider some hardier material such as crushed concrete instead of gravel and dirt. I got a quote for a Park I had under contract for 2 inches of asphalt overlay and around 450 feet of road and the quote was something like 60K. This was only a 25 pad park. Gravel and crushed concrete is pretty cheap and a fine tactical approach until you get the Park turned around.
For establishing lot rent I would look at the competition to see what they're charging, combined with the condition of the homes and capital expenditures needed. Personally I would set lot rent at the bottom of the market, and if the POH's are in bad shape, tons of trees need trimming, water lines replaced, etc I would deduct even further to reflect that, or alternatively estimate the repairs as a one time offset towards the sale price. Either works and the conversation with the Seller is the same and you can be transparent about it.
I always get permission to interview the tenants during diligence. Just ask them. Sometimes Sellers won't allow you to interview them at which point I just assume that you will have to non renew most of their leases, repair, and resell. If the test ad does well and you can afford rehabbing the units it's a non-issue.
How many acres is the Park? If it's 0.25 then that seems like a lot of entrances and maybe close one off, but if it's 5 acres I wouldn't worry about it. I have seen a 0.75 acre Park with 12 homes and 3 entrances. 3 was too many, but not a deal killer.