I just picked the cheapest, closest cage builder who’s done se30s and let him do it how he wanted. I actually didn’t know it was legal to run tubes in the trunk at the time. I went to Chris schimmel “Competition Cages” in hillsborough, NC. Cost me 18 something including removing the sunroof cassette, a dash bar, and nascar door bars almost tight up to the outer door skin on the driver’s side. He also put in the window net included in that price. I think I posted pictures on this forum somewhere.
Get your racing seat mounted where you want it and take your window and right side net with to the cage builder so they can weld that stuff where it needs to go instead of guessing how what you buy is going to mount. If your going to lower your steering column you should do that also before you get the cage put in. If the cage builder is far away ask about leaving the trailer there while it’s being built. I made the assumption I could leave it but his yard is to small, so he has to arrange it with a neighbor.