To me and my build it came down to strength. Adding reinforcement to the seams (as in glued cloth strips) made sense to aid in keeping that joint tight and secure. I used bedsheet to stay thin, yet still add strength as the reinforcement at the seams. The canvas/cloth over also laps the seam adding yet another layer of strength.
I wasn't sure how much of an effect layering the entire side with canvas/cloth would do, so it surprised me as to how much it did indeed add.
Your question leads to wondering if the foam itself is strong enough to perform under real conditions. My guess is probably, yet I do see how it could crack or split at the seams from just running down the road. Going the route of skinning and reinforcing the seams just adds durability to your project! I'm certain you want it to last years of service.
