Hello from a fellow trailer tower.
IF (note I use the big IF) you had a clean slate, you could build a functional popup style trailer that lowers right down over the Miata, but pops up when you get to the track. I know, probably out of the time and $$$ budget, but this is the place to dream, right?
Can you enclose the trailer tires with skirts?
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2007 Dodge Ram 3500 SRW 4x4 with 6MT
2003 TDI Beetle
2002 TDI Beetle
currently parked - 1996 Dodge 2500 Cummins Turbodiesel
Custom cab, auto, 3.55 gears