In reply to Nicola:
I believe Le Vaudoué (Potala, Rocher fin, Diplodocus etc) has no height restriction and I guess safe. Franchard is off. Roche aux Sabots/Cul de chien is OK if you park right before the overhead barrier (on your right), that's where coaches park (no idea whether it's only for coaches though, but I doubt it?). I've seen shattered glass there recently though. Apremont is OK too and I guess safe. Bois Rond is OK (roadside though so may be less safe?). I'm 99% sure JA Martin is fine too. I'm not sure about 95.2 but I think it's OK (the carpark is easily cramped though so manoeuvring with a motorhome may not be much fun if it's packed, which it will be any weekend starting now). Canche aux Merciers has no overhead barriers but you drive under the highway and I don't know how high the tunnel is. Dame Jouanne is OK, Elephant may be too if you park roadside but part of it is reserved for coaches.
Just saw you're going in May: it's going to be ridiculously busy (holidays, bank holidays, Bavarian holidays, etc) so you'll want to go early to find a spot at some of these areas, like Sabots (the carpark will be overflowing on the road by noon if it's a sunny weekend or French bank holiday).
Post edited at 18:44