How would you sort the rust on this trailer?

[Kilo]

That; for maybe £300, versus faffing about getting filthy with a grinder for hours then mithering over several coats of paint.

£300 for blasting & dipping? Where are these people? Don't forget to add onto that equation the half day + at either end of the process getting it there, prepping it, putting it all back together & driving it home.

 

[Caraway]

Yes.
It's the same equation I use when I need (or would like) to go to town and get some more cuttings discs to finish something I am doing.
Yes, it would be more awkward to spend the next half an hour filing or sawing some 6mm steel plate. But in 30 minutes it will be done, whereas getting the discs will take about 90 minutes, including cleaning up, changing, driving, etc. etc.
And doing it manually will be free.
£2 worth of fuel and the cutting discs will raise the cost to £10, for a longer job.

 

[JumbleDuck]

Really not worth shot blasting & dipping unless you're planning to keep the boat for a good long while. Even at today's inflated prices the process will cost more than its worth. Best return is a quick spruce up, ensure it's roadworthy (sounds like you've done that) so that potential buyers are able to drive away with the boat trailing behind & job done.

Last time I had some stuff galvanised I was charged 50p per kilogram (of steel). Trailers are expensive!

 

[JumbleDuck]

£300 for blasting & dipping? Where are these people? Don't forget to add onto that equation the half day + at either end of the process getting it there, prepping it, putting it all back together & driving it home.

It's going to need dismantled, reassembled and a hell of a lot more work in between if it's wire-brushed and painted. My local galvanisers are a hundred miles away, but they collect from local fabricators and blacksmiths every week, so getting stuff to them is easy.

I had the parts of a trailer for a classic dinghy dipped a few years ago. Cost me about £40, iirc.

 

[Kilo]

It's going to need dismantled, reassembled and a hell of a lot more work in between if it's wire-brushed and painted. My local galvanisers are a hundred miles away, but they collect from local fabricators and blacksmiths every week, so getting stuff to them is easy.

I had the parts of a trailer for a classic dinghy dipped a few years ago. Cost me about £40, iirc.

?Yup at that price probably is worth investigating but nothing near me or collected locally has ever been that cheap. Added to which most dinghy trailers are featherweights compared to Steve's trailer.

 

[PaulRainbow]

Yes.
It's the same equation I use when I need (or would like) to go to town and get some more cuttings discs to finish something I am doing.
Yes, it would be more awkward to spend the next half an hour filing or sawing some 6mm steel plate. But in 30 minutes it will be done, whereas getting the discs will take about 90 minutes, including cleaning up, changing, driving, etc. etc.
And doing it manually will be free.
£2 worth of fuel and the cutting discs will raise the cost to £10, for a longer job.

You obviously need a better stock control system, something more efficient than filing

 

[John the kiwi]

Shot blast and arc spray with zinc.
This method is equivalent to hot dip but limited to open sections which you seem to have.

I built the trailer for my 26 ft trailer yacht from channel sections specifically so i could use this method as Hot dip facility was 200 miles away.
I found 3 companies that could do this near me and it cost less than hot dip.
The company I chose offered great service and 4 years later i am still pleased.
The trailer is almost fully submerged in seawater each time i launch and retrieve, which is at least 20-30 times per year.
Dissassembly is not totally necessary. Touch ups are possible! No paint system is going to compete.

In previous life as Engineering /maintenance manager, I had forklift relocatable steel platforms blasted and sprayed . The platforms were bashed by forklifts and lived outside in the elements and the zinc spray worked brilliantly!