That's so funny about her reaction to the new pad, did you try doing any CT to get her more comfortable with it? Targeting it and having it rubbed on her?
That is funny with the muck pile :P Whenever our dumpster guy takes my dumpster away the horses are always astounded by the empty spot in the driveway xD but my mare has done amazingly well with the dumpster, I had her targetting it and putting a foot on the loud metal and doing great with CT near it - hopefully it'll help her be comfortable with trailers in the future (but of course she only touches the dumpster doesn't stand on it).
I always kind of understood keeping them under their threshold, but a lot of the training I'd seen (traditional and natural) encouraged horses to go over their threshold, get all worked up and then settle down. Learning that it was easier to deal quietly with the scary thing than to work when they're acting nervous. But with Tank in particular she doesn't come back down off that high for a great deal of time - and not while the concern is still present. So to work her up to her fear and rewarding for the correct responses was always much better than pushing her over her limit and bringing her back down. :)