25 pdr Carriage construction

[Michael J Hine]

Can someone explain how the real box section carriage was riveted together with conventional rivets?

I can see how blind rivets could be used but how was an anvil placed inside the box sections of the carriage trails to enable conventional riveting?

I ask since I am contemplating fabricating the trails from sheet steel. The alternative is to make it of welded construction like the Australian example already mentioned on the Forum.