Outer Limits 4x4 Board

I have a troopy and am looking at getting a tinnie to put up top.

If anyone has done this my question is how much difference did u notice in fuel economy? And was the any notable difference in on road driving and fuel economy?

Thank you all for you help

Ive had my tinny up top a few times and it made bugger all difference
to the handling but not to sure about L per 100kms

My tinny is about 55kgs 10ft Quintrex