I haven't read all of the replies, so if this has already been mentioned I apologize.
Regarding putting the dump bed in the front of the trailer and doing a side dump... Have you figured out ow much clearance between the ground and the the bottom of the bin while its in the up position? Generally with low clearances (like a trailer opposed to a truck) you would need to dump then pull forward in order to empty the bin. I dont see how oyu would be able to do this when dumping to the side.
16 years experience, 10 as owner/operator.
And still not rich