No, but. there is an inner arch you should be able to feel. So it will feel like it is double skinned, you have problems if you can feel three!
Theres the arch tub then the outer arch But yes many busses are doubled skinned on the rear arches because the old way of doing things Was to slap the new arch over the top of the old one Tack it into place then hammer it in a bit and clag it with filler Ive see a bus once that had 3 arches over the top of the rotten one which had patches on it aswell
