George, I made it to Tumwater in the rain and wind 69 miles no problem. I took Aurora, 599, then on to I-5. It's far less hilly along the Duwamish heading south.
Do you ever go thru a carwash? Is it an aerodynamic cavitation effect eating at it? That is strange and I'm with you keeping my Leaf as factory fresh as I can. That makes parking tough but worth it to me.
"No elevation" is not true, there are plenty of big hills on that trip. 100% would do it if you are good.
I base that on my experience and experiment of driving the Lake Washington Loop I-5 and 405 at freeway speed (68 mile trip for me)
Getting a 100% charge in Burlington could be a nuisance to...
I installed my kit in less than 1/2 hour! Real simple. The back up cam controlled by my mirror button is real handy for lane changes in thick traffic.
It's very well made and worth it if you want these features. :D