Help please! Van has died

"Derelict" does seem a rather untechnical term for a 'technician' to use!

I would agree with those who have suggested getting it looked at elsewhere.

We have had to have several lots of welding done over the years to pass MOTs and the experience has varied depending on the garages used. 

Some have had no welding facilities whatsoever and the vehicle has had to be taken elsewhere that had, either with the capability to also then do a fresh MOT (paid for) or else the vehicle was taken back to the original MOT station for a retest (free).

Others have had no inhouse welders but have had an arrangement with a local specialist to come in and work on the vehicle in their workshop, which has the capability to cope with high vehicles, after which the vehicle can be retested.

The garage we have used for services and MOTs for the past few years do have inhouse welding capability although there has sometimes been delays in fitting in the work needed to pass.

The poor undersealing hasn't solved the problem - better to get someone who knows what they are doing to deal with it properly.

Even if it means spending some money on it, in my opinion the hab conversions of AS vans of that era are so much better than later models and in view of the difference in purchase costs to replace it, I believe it to be an investment to do what is needed to keep it going hopefully for another few years.