Tunnel into Zion--how difficult or alternative?

It's not difficult at all. A ranger will collect the fee before you enter the tunnel. Traffic is stopped so that it's essentially a one way road through the tunnel. When we did it in the spring two years ago there were enough people going through that we had to wait in line for maybe 10 - 15 minutes. Then everyone goes through at once, cars and RVs. The only alternative is to drive all the way around outside the park.