I think you can do a pretty good inspection of the upper tubes with a mirror on a stick and a strong light. That said you do need to have a good idea of what you are looking for and exactly where. There are some good photos on this forum of fractured chassis tubes but they do start small. I think they probably propagate quite quickly, so not many photos of the crack starting and that also suggests you maybe need to be looking fairly frequently.

This is one of the few early crack photos I know of. Its near the back bracket of the upper wishbone aft mount, just to give anyone an idea of where to check.

[Linked Image]