Looks like there is plenty of room on either side but have not seen one.

it's a F700 with a 10 ft dump bed .

Any Ideas ?

 

About any under body box will work. Make a set of L brackets out of angle iron (2" works good), bolt the brackets to the truck frame with the flat side toward each other at the correct distance for box length then bolt the box on to the brackets. Some companies offer mounting bracket kits.

 

Thanks, that's what I needed.