Atsugi: no ladder needed, just climb the spotters hill (bring mm's though) and/or find yourself a good spot in the final approach.
Hyakuri: I think a ladder is still needed here, although I don't know how things have changed lately. How do you plan to get here by public transport by the way?
At Hyakuri you don't need a stepladder, go to the gate for the towers and phone the number which is at the gate.An old lady will come and after payment you can go to the towers, which is really a perfect place for taxi shots and shots on the runway.From there even shots at the platform are possible.Good luck
To Hyakuri A.B..
When you use the bus from JR Tokyo Station(Yaesu Exit) to Ibaraki airport(Hyakuri AB),
the 1st. bus Dep.0810, Arr. 0950(1,000Jpy).
But there is no buses from airport to the base gate or Opp. site.
There are some taxies at the airport, but the fare is about 2,000-3,000Jpy in one way.
So I think you had better to rent a car at Tokyo area.(6,500-12,000JPY/24Hrs.)
To Atsugi:
You will not need the JR pass because you'll use one the private lines(Not JR lines).
***To the North side of Atsugi***:
Shinjuku--(Odakyu-Enosima line, Express.)--Yamato Sta.--walk 20min.
Yokohama--(Sotetsu line, Express.)--(via Yamato Sta.)--SagamiOtsuka Sta., walk 15 min.
***To the South side of Atsugi***
Shinjuku--(Odakyu-Enosima line, Express.)--(at the Yamato Sta. exchange to the local train)--Sakuragaoka --walk 20min.
Yokohama--(Sotetsu line, Express.)--Yamato Sta. exchange to Odakyu-Enoshima-line, Local--
--Sakuragaoka Sta.,-- walk 20 min.
1st visit for me too. But apparently the are enough hardware stores around the Narita area to buy step ladders. If you go to googleearth and zoom in on Narita. Type in "hardware store" in the search and voila. The are a couple of stores you can see in streetview as well, sporting many step ladders