I use a bolt through the toolbox and the siderail of the truck (one on each side) but I don't put a nut on it. Instead I have hitchpin clips. That way I can quickly take the toolbox off if I need the extra room. I put the bolts up through from underneath with the clips inside so they can't be removed if the box is locked.
__________________
'85 ATC250R
.030 Over Wiseco
FMF Pipe/Answer silencer
36PJ Keihin
K&N
Boyesen reeds
Magura hydraulic clutch
Roost Boost
MSR bars
OMF swingarm skid
ITP Beadlocks
Three Wheelin' Since '84