Piston Junction is coming along.

Well this strategy is used more with single lane hot wheels tracks but could be useful. it's called pinching and flaring. Basically you pinch the first piece of sidewall inwards, where the cars come through, then flare the end of sidewall on the part where the cars exit each piece of track. The idea is by pinching and flaring the entries and exits of each piece of track you are giving each car a cleaner entrance between each piece of track so that they aren't potentially nicking the parts where the tracks connect on the sides. Again this is commonly used with single lane hot wheels track so I don't know if it works with fat track

I would suggest, flat rigidness is needed under the track.  The crash track I've played with is very floppy, and resists holding a uniform shape consistantly.  
If you look at the pic above, this is what I was fighting.  The connector holds the track shape only to have it flatten out right after.  I used extra (slanman) connectors in the track before and after and it at least lengthened the transition, and helped a ton.  When I finally build the big track, I planned on using some sort of rigid (probably 18-16 ga sheet metal) pieces to hold the sidewalls straighter and truer, and secure with 1" washers in the center (diagram below)

dr

Track is looking great!  Can't wait to see it finished and ready for action.

The track is looking really good. Excited to see the finished product. If you plan on hosting mail-in races make be sure you're tuning track to work with cars modified for speed. My experience with my home track was what worked with stock cars made my track too fast for modifieds and they were struggling to finish without DNFing.