Make sure you stop drill all the cracks at the end, then add your doubler. Clamp doubler on then predrill all holes. Then I suggest putting epoxy between booth pieces of aluminium and rivet away.
I also suggest that you do both sides rather than one. This will give you equal stress points on the whole tunnel.
This will then be the strongest piece on the sled.
You will then have no issues hauling fuel or bending again.