bulding a mini sand rail

[mach1]

so Im going to build a sand rail but one that is aboutn the size of a 600cc go kart. Im going to be using round tubing for the frame but unsure if I use hollow or filled tubing and if hollow what wall thickness? also Im not sure if its called a sand rail or ATV or go kart but its a one seater 2wd sporting either a GS motor or a Gixxer motor.