In honesty guys there really is not a need to run stem to stern with 2.5 box. Tremendous overkill. As long as it gets near the 1/3 area of the box you are fine, Most car trailer manufactureres do that.
I think System f stated he was plating the botton of the trailer. If so it will be strong enough with the steel he is adding if not jointing at the front wall. I will say the two added struts running from the front tube to the tongue add very little benefit to the strength of the trailer. . You will need to protect the tanks I think, but it depends on the heigth of the lower trailer. I just did mine with out skids due to the torflex axle protecting them and that they are in the frame 24 inches up.
I think System f stated he was plating the botton of the trailer. If so it will be strong enough with the steel he is adding if not jointing at the front wall. I will say the two added struts running from the front tube to the tongue add very little benefit to the strength of the trailer. . You will need to protect the tanks I think, but it depends on the heigth of the lower trailer. I just did mine with out skids due to the torflex axle protecting them and that they are in the frame 24 inches up.