regardless of the strength of the epoxy the connection to the other body component is the weak link.

when you weld in a panel its becoming a piece of the original, not attached to it. West Sys. is good stuff but even if you cant afford to pay a welder you can buy a cheap mig gas welder at Harbor Frt. & get away with that - west system isn't cheap stuff & likely when you hit the first bump in the road you'll crack at the weak points then you'll be doing it all over again. For me thats worse. On boats epoxy laminates of wood with vacuum bagged epoxy are extremely strong but thats because the epoxy is drawn into the wood fiber & becomes "one" with the layers thus creating the strength, kind of like welding.
Good luck with the project.