Will try it your way Tug. As it happens I was adjusting rear wheels brakes ready for MOT this month, whipped of wheel to make job easier and to my horror found that the bottom of the spring had eaten almost completely through the tubular retaining piece on swing axle/trailing arm,. Barely a tiny bit of metal holding it there. Mercdoctor walked past, peered over my shoulder in that all-knowing and direct manner of his and said "That's f%^&ed mate" and reappeared with a good second hand trailing arm, muttering something about eating VW probs for breakfast and to get on with it!
Anyway, old bushes on s/h one were removed yesterday with an acetalene torch (outer bolt seized solid in bush) and arm has gone off to be shot blasted and primed. New bushes are in the post. In the meantime I'm driving around like I had loose eggs on the back seat until arm is replaced sometime next week.
On top of that, one of the top washers on front drop links has decided to depart company and go up about three inches meaning I have to go almost to a stop to negate any sharp corner. Feels like I'm driving a ruddy milk float at the moment.
The trailing arm thats coming off, other than holes under the spring plate, could I'm sure be put back into service with a new piece of metal added as shown above. Unfortunately they can rot right through on top and even Baxter's replacement spring retainer may not be enough to salvage a damaged arm. Clearly some have more extensive rust and need a more substantial piece welded beneath this plate.
Marcus and I did discuss the galvanizing idea but felt it was overkill as they'd probably outlast entire van by 100 to 1. Good shotblast, two pack chassis black and underseal will be enough for me. The world will have run out of oil or the T25 outlawed by regulation long before they give up the ghost.

- not a criticsm of the idea as its a very sensible one but just don't see its really needed in this particular instance. Mind you. I always felt bug heater channels should be galvanized and I think treating wheels this way is excellent!!