Styrene Tool box

[SonoranWraith]

Is that squadron? Avoid that stuff it shrinks and cracks. You should get your styrene joints as tight as possible. It looks like you have square backer rod in there so if you were to sand through the sheet to get the rounded corner look you want you would be exposing/shaping the rod behind. Interesting use of whatever building kit the support is, but you might just make that out of styrene too, it comes in a lot of profile shapes.