Originally Posted by Poly
I'm not sure where you are making the distinction between a rubber dinghy and a SIB; before RIBnet* coined the phrase SIB there were only inflatable boats... I assume you are really talking about children's beach toys but I have no idea why one couldn't be transported inflated if you chose to and tied it down safely.
*there is some suggestion that the Scandinavians might have started it, but I prefer to think it was Keith (don't forget the brackets) Hart.
I'd say a SIB is a bona fide boat that is inflatable, whereas a rubber dinghy is, if not a beach toy, not really a practical boat - the sort of thing you see for sale at the seaside rather than at a marina or chandlery.
However, there are "rubber dinghies" sold as suitable for 3 or 4 people and I'm sure some people are tempted to take them beyond their design remit. I have seen "rubber dinghies" on roof racks (rather than trailers) bending upwards and folding because of the headwind. However, a "proper SIB" (as we would understand the term) properly inflated has enough rigidity for this to be unlikely.
I mentioned "rubber dinghies" for completeness because the original poster seemed to be unsure of definitions. On eBay you may well find items misdescribed. In another forum I use, a novice bought a musical instrument only to find it was a completely different type from what it was listed as.