Thanks John. Just come from checking in the garage. There are in fact six drain/vents. One each side at the front half way up as drains seemingly for the rotary fan housing and two lower at back and each side. The lowest of these seems an adequate drain for the air inlet chamber so will leave as is.
I then checked with my head in each footwell. No further drains seen although I can feel significant holes in the back of warm air outlet box which makes a farce of shutting the air vents
A powerful lamp shining through front vents allowed me to see the heat control flap was shutting fully though.
ETA: just seen your very helpful picture Rog. May check again but those drain tubes appear to be hidden on the 3.7 Roadster given the width of transmission tunnel. Might be visible from underneath with a torch. Will check later.
