I have recently acquired a galvanised dingy trailer that is 1) fairly old and 2) has probably sat with way over the design weight on it for many years , and so the 4 (x2) rubber rods that make up the 'independent suspension' have been over-compressed / distorted and so 3) the ride height has been compromised (tyres very close to the inside of the mudguards) and 4) the 'suspension' (ride / travel) has also been compromised.
I don't think it's likely to catastrophically fail / collapse as it looks like the rubbers just get squashed flat(er), however, it's not ideal. This sort of thing:
Now, in many cases these suspension units are independent (of the trailer chassis) and so can be replaced easily. In this case they are part of the actual chassis and so not so easy to replace.
(If I was to replace them I would have to first remove the old units and then grind back the galv, then weld plates to the underside of the box section to allow fitment of standard independent units and re protect with cold galv etc).
Now, assuming I could get the old arms out of the box section (drill, Porta Press) and could find the right rubber (section, material, elasticity) I could (hypothetically) press the arms with new rubbers back in.
However, I'm not sure that is how they make them, or how some make them new and I think I read somewhere that they might first stretch the rubber rods (reducing the section), then they are frozen (temporarily 'locking' the reduced section) and then the rods and arm inserted into the tube where the rods then defrost, regain their full section and hold the arm in place. ;-)
An alternative thought was that years ago a mate had a large tub of some (nasty) liquid that he dropped some of my hardened rubber bits into (4 motorcycle carb inlet rubbers) for a few seconds, pulled them out and rinsed them off and they were all rubbery again? ;-) Anyone know what that liquid might have been?
A final / compromise solution would be to fabricate some sort of adapter that would both bolt onto the original trailer axle and then allow the new suspension units to bolt onto that, saving the issue of having to extract the old suspension stuff (I can just cut the old arm off) and remove the galv to weld etc.
As an aside to the main question I would be looking for what they refer to as '200kg units' (so 100kg each) because the trailer gross weight is 180kg and as a typical 14' (or less) boat that I might have on their weighs between 50-100kg, I don't want the suspension to stiff (been there before). You can easily buy 200kg units bit not with such a good range of designs (and so 'rides') as the heavier units.
Cheers, T i m
 There has been a 14' dinghy sitting on the trailer for ~11 years that I know of and the boat itself weighs about 75kg. However, with all the other bits that were left in there it could have been nearer 100. The real issue though is for some of that time the boat also had quite a bit of water in it, possibly at least 1/2 a cubic metre and so that was an *additional* ~500kg sitting on the suspension units! ;-(
p.s. I wonder now the trailer is unloaded the suspension rubbers might recover to some degree (over the next 11+ years), and if that could be improved if I was to apply some negative pressure to the units?