I admit I had to look that up. It looks like "side loader" is a shipping container without wheels that can be loaded onto various transportation such as train (rails), truck (highways), or ship (ocean). My understanding of a "trailer" is a wheeled container that hitches to the back of a semi-truck and is hauled along the highway. So maybe the difference is cost? The containers appear to be of similar size and construction. Good luck!

"trailer for side loader" please copy and paste this url below in your address bar. https://www.google.co.in/search?q=trailer+for+side+loader&client=firefox-a&hs=FCz&rls=org.mozilla:en-US:official&source=lnms&tbm=isch&sa=X&ei=6mZbU5WPGcmUrge_soCABA&ved=0CAcQ_AUoAg&biw=1440&bih=761#facrc=_&imgdii=_&imgrc=JdzgzWrbEmy8pM%253A%3Bxm4_FhyShjNi2M%3Bhttp%253A%252F%252Fwww.1-87vehicles.org%252Fimages%252FKenworth%252Fk100_daycab_wht-blu_sideloader_rf_lg.jpg%3Bhttp%253A%252F%252Fwww.1-87vehicles.org%252Fphoto507%252Fkw_k100_daycab_sideloader_rfl.php%3B800%3B445