Think you'll find that most, if not all, of the racing regulating bodies ban the use of any aerodynamic aids on the underside of the car.
From the BRCA 1:10 TC section;
6.4 Under body/chassis aerodynamic aids of any
nature are not allowed. Only motor guards are
allowed. Smooth lexan undertrays may be fitted
to waterproof the cars.
Xray T4'16, T4'14 (Wet Car)
Xray X12 2016
wlrc.co.uk (West London Racing Centre)