I'm thinking Single Speed Trykes are more for boardwalk rides than anything with an incline. My concern would not be so much about being able to peddle the hill but how your knees are going to feel after hours of crunching up inclines. From a set back seated positon it would be hard to stand to peddle which is how you would get yourself over a hill or incline on a two wheeled single speed.

One option would be to put a peddle assist hub on it to "level out" any incline. I'm thingking like the Bionx hub that will augment your peddling, not one of the cheaper E-hubs that would make it a motorized tryke but just it a little boost......but then it woudl be cheaper and better to just buy a geared tryke from the get-go.