Making the first sub tunnel modules in O now over 20 years ago, they are hard to view down low. They remain packed up back in Nashville and for sale. Moving to Fl. I have no room anymore for them. All G.G. Stainless trackage, another must to have trouble free operation.
I would suggest having the tops open so you can look down or rising them up to standing eye level.
Retrofits to existing layouts simply don't work. Need to be designed and thought out from the beginning.
There are many unforeseen logistics as well. Just my experience.
If you are just doing an above ground EL, that's easier.