How much of a discount for dirt roads?

I just started looking at a small mobile home park (about 35 occupied lots) with dirt roads. How does that change the valuation? I usually use Frank’s method:

(Lot Rent x 12 x .7 or .6 x # of Occupied Lots) / Cap Rate

Would it just increase the cap rate? How many points? Could I just subtract out the cost of paving the roads? Could this be a value-add opportunity - has anyone done this?

I’m also assuming it would be harder to finance with dirt roads.

Thanks in advance to those that have seen something similar.