Details (age, make, model and photos) of the old motorhome being restored would be useful, as would photos of the gas heater itself (as Damian has said above).
Unsurprisingly there seems to be no reliable on-line information about a Rondo Vector appliance, though I think it might have been a wall-mounted ‘instant’ water heater of the type that was commonly fitted years ago.
Your best bet for advice is likely to be from an 'old campervan’ group - for example
As Underwood suggests, I think it may have been an instantaneous water heater, and if it was, then you really need to carefully consider whether it should be revived or not. Present legislation has virtually outlawed the older types of instantaneous water heaters becasue of a couple of safety issues. Most were what were called open flue products, and that means they can discharge their products of combustion directly into the living space, and becasue of the crudeness of their combustion, those products can be laden with large amounts of Carbon Monoxide.
Modern counterparts have to be room sealed, and unfortunately that often restricts them for providing instantaneous hot water, so you perhaps should consider a storage water heater instead.