I've been through Leavenworth maybe a dozen times in the past 20 years. I would not call the designated RV parking area "HUGE." Your 34 footer should be OK but I have seen that lot packed with trucks, RV's, construction equipment or just roped off for a local event that needed some designated parking area.
Perhaps a call to their Chamber of Commerce or visitor's center or equivalent will give you the current status of RV parking in their city.
It is a fun place to visit.