Build the sides as high as you can. On my dump insert I built 5' high sides which still allows me to get under most bridges around town.
Id also suggest looking into getting a extension piece for the loader to get the discharge chute high up then it is. I bought a 24" extension for my Billy Goat loader and it worked perfect.
Go to Harbor Freight and get a mesh tarp for the top. It keeps all the debris in but allows enough airflow to compact everything inside the box.
2004 Ford F250 Super Duty V8 4x4 w/EZ Dumper
Fisher 8' HD plow
2009 Scag Turf Tiger 61" 29DFI w/collection system
2007 Exmark 48" Turf Tracer HP 17hp
2 Shindaiwa Trimmers
Echo T755-H Backpack plower
6x14' Big Tex Open Trailer
Little Wonder 10hp blower
Echo T-150 Hedge Trimmer