wdyt? fear of public restrooms or stubborn?

DS is doing pretty well with PTing, considering his age, I think. He does better at weekends, when there are two parents to notice his hints, and when we're based at home more. Last week H was away, and I dont' know if it was that (he was generally a cranky little boy while Daddy was away), the fact that we were out and about a lot (to preserve my sanity) or something else, but PTing went downhill from Wednesday aftenroon onwards. I was getting desperate, thinking that maybe his successes last weekend (no accidents and not telling us, but compliant to sitting on the potty when we said) were a fluke, and that he wasn't ready yet. But then yesterday he told us he needed a wee, and then (as it happened) a poo. And today, despite a couple substantial accidents, he told us three times that he needed to go, and actually held on for 15 min in the car in traffic.

But... while we were out, he refused to go. He screams at the thought of entering a public bathroom. He has always been nervous of hand dryers, but it's getting really bad now for some reason. Even when we assure him we're the only ones in there (in a disabled restroom, e.g.), he freaks, screams, etc. And if I do get him to sit down, he gets upset and says 'no pee'. Obviously he cold just be telling me he doesn't need to pee, but it's so hard to know if he's scared, doesn't need to pee, or is just stubborn.

I bowed to the disposable diaper gods today and he wore Bob the Builder pull ups to nursery school, refused to go to the potty there, but did wet them. I put on training pants (cotton) after, and he stayed dry (more or less) for 3+ hours (including two ill-fated attempts to get him to go with me in public restrooms), and then was 4 for 1 with telling us v. accidents.

Do I just relax, put him in trainers or pull ups when out, and focus on letting him tell me if he needs to go, but don't try to take him otherwise? What do you think?