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I wouldn't quite agree with Mike on point 4. "Trailer Tyres" or light truck tyres were necessary for him as he was in the unusual position of having a Dandy 6 on 10" wheels. With 12" wheels on 6's and 10" on everything else car tyres have adequate load capacity. Unless there is evidence of recently replaced tyres I would always budget for new ones.
As Mike said the floor being songy is one big problem. It can be fixed (all Dandy faults can be fixed) but it's a serious job.
Next up is the chassis. Is there corrosion if so how bad?
Nearly all brakes just need adjustment. If however parts are missing from the brakes then pre 1989 brake parts are expensive. You could conceivably have rod brakes and spares for these are not easy to find. If complete though adjustment may be adequate for 20 years+ so no panic if complete.
Orange/Yellow Dandys can be found with phenolic ply trailer (tub) sides or plastic ones. Unless you are very lucky the ply will be getting past its best on the bottom edge. The plastic sides tend to warp and are probably the least loved material for sides.
Why are you looking at this? Is it desperately cheap or do you want to use it with a 70's car? If cheapness is the driving force I'd if you bide your time almost any pre 1990 Dandy Brown and earlier can be found for less than £500. It's very easy to spend several hundred if faults are found.
On the other hand the Orange/Yellow is a lovely vibrant colour and minor issues like warped tub sides don't stop you from enjoying the camper. Also Dandys are very resilient it could be very easy for an almost pristine example to be rolled out of a garage. Though not pristine I have a 40+ year old Dandy.
Might be a bit much for you but if you think saying "anything can be fixed" might be an exaggeration see what Phoenix did with his old 4: [You must be registered and logged in to see this link.]
What type of Dandy (4, 41/2, 5 or 6) does it have an awning? The awnings on early Dandys offer a bit less space than on later ones but are easier to put up.