That does not look like an enclosed shower ... it looks more like someone glued laminate or some kind of plastic sheet on a wall.
I've never seen anything but completely enclosed shower unit in Lance. I've seen others like this (other Mfgrs) , where someone (owner, or the Mfgr) added or modified a shower with 'laminate sheeting' ... but laminate sheeting will not flex like that, it might bow, but not bubble like that.
If it were me selling it, and it 'unflexed' when it cooled off, doncha think I'd take a photo of it when it was 'unflexed', instead of like it is ...
Based on that specific image, I'd think very long and hard about that shower and how much trouble it might give you later. It certainly looks more like in the wall bubbles to me, rather than a heat-flex like the seller claims.
If it's there, behind the shower, and if it's 'moisture caused' no telling where else it might be in the walls too. My personal take, it's moisture inside or behind that wall -- and only say that because that's what moisture would do, as opposed to what heat-flexing would do. JMHO ... M44
ON EDIT: If the deal is good enough, I'd plan on removing that entire shower and seeing what it is, and than re-doing that shower in a way that eliminates that flex. If the pan is good, it's not a difficult process, but labor intensive ... probably not material expensive unless you find damage behind it. But in any case, I'd not leave it, I'd figure it out and fix it if I bought the camper.
