My concern would be how much back flow you will have due to the tight 90 and what looks like 4 inch round. I would definitely be testing that with a good 4 hour run. From everyone I talked to when building my trailer they said to use atleast 8 inch round.
I was also told at least an 8" exhaust for the burner and all the exhausts I have seen for burners have been at least 8" or larger.
I think Russ or Paul K. would know for sure.
That does look like a nice setup, very professional, am I seeing some floor by the tank that did not get the black coating or is it my imagination?
What brand of skid is that Gene?