(4) Base Camp
This book shouldn't stump you too much. On the one hand, it moves back and forth in time, with an aging narrator who sometimes forgets where and when he is. And in the scenes set in the past, there is a good amount of period language, which isn't super clear for those us who aren't familiar with the 1930s. (Which, let's face it, most of us aren't.)
On the other hand, the story is generally straightforward and told in the present tense. This makes it easy to get caught up in, and turns it into a page-turning easy read.
Finally, at least in Shmoop's paperback copy, each chapter begins with a great, evocative illustration of circus folk. These help draw us in and give us a sense of what the characters might have looked like (our imaginations can do the rest of the work).