As for tension, yeah it's a little high. That's a good callout.
Maybe something like two hook assemblies that engage over the horizontal webbing on the vehicle frame on the top and bottom.Then those bolt onto the vertical support.
The hooks could be the 2x3 channel, back to back, with a spacer welded in the middle to account for the flange thickness of the frame.
That way the diagonal stringer pulls at a more rational angle and keeps the tension down.
So similar to a chassis frame bracket, but with a tie in the middle to lend more strength.
I am very averse to drilling holes in the frame in the middle of the bus.
The diagonal support can then run from the very top of the frame rail
Originally Posted by family wagon
That'll help pull the center of gravity back down after it was raised with the roof! Wow, that's (relatively) a lot of tension on the diagonals and compression on the segment at bottom between the tanks. At least to me it seems like it should be a lot. I can't quite read what channel you picked for it.. is that C with 2" flange, 3" web, and ?? thickness?
I was having tank envy at first (I have just two 42 gallon fresh) but since you clarified half of yours are for waste I feel better.