you need to tackle the inside of the framing if youre going to make a meaningful difference to the longevity of the trailer

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the applicator wands will help you get up inside the frame from the drain holes 

Been doing this on all our trailers for 35/40 odd yrs. Scored 2 X5L containers lanocoate grease way back then. Our boat trailer is 40yrs old  yet to have a weld repair other than couple mud guard support ripped on a fence post.

 Trailers are well washed and water blast then let dry for few days.

 If any surface rust, wire brush and phosphoric acid (rust kill) without the white epoxy additive.

 Do not put the acid on any good galve areas, it eats the galv.

 I 1/2 fill a jam jar with lanocoate grease and near fill with turps/ kero. With old brush slowly build up a soln of grease about 1/2 the jar.

Then paint well into springs back of wheels hubs etc. Remove the wheels , makes access for painting and spraying easy later.

Using a elcheapo super cheap panel beaters body under spray gun.. has a spay tube about 10/12".... 1/3 fill gun with lanocoate soln and top off with turps....I have topped off with fisholene fliud before.. cause 'was there'

My box chassis chassis rails are open each end

Important: hand a rag over the other end of the chassis rail from end going to spray do not then lanocoate will end up over the cars, neighbours windows.

Spray up one end the from the other, doesnt take much.

Spray chassis cross members , springs etc. forcing what hasa been painted further into springs and crevasses.

 Whole process takes about 20 min not including painting springs.

 Do not spray winches .

It remains tacky for a while..

 After couple days in the sun its just tacky...doesnt pick up dust etc, but do not go over dusty metal roads for a week or so.

It leaves a slightly brown ting to the trailer.. not pretty but on the other had becomes a point of conservation as what it is and that the trailer is actually cared for.

I have tried the lanocoate in a can .. you will use a lot cans and just doesnt get deep in places really needs it, like a gun and compressor...and stays tacky far longer

Down side.. bit of over spray on the hull.. not really noticeable, but if fussy wipes off easy with bit turps and rags.

So thats 30 odd yrs of actual real hands on personal trial and error experience, and results, originally based on my grandfather spraying his farm machinery with waste oil in the 1950s and before.

 Hope some may find it usefull.

I believe there are some trailer manufactures and ppl who repair offer a similar 'after market service' . like buy a new car and they offer to put special protection over the paint and upholstery..

But yes I go along with what you say.. its like selling life jackets with out crotch straps.. an after market addon.

If I'd just bought a super yacht, it wouldn't have been an issue either.  

Good practice regardless if galv or alloy

 Funny you mentioned that.. one of my regular crew is an engineer, few yrs was fascinated at the mareati club ramp ramp by several of the alloy trailers.. mumbling about anelling welds , correct alloy /stress and lot other stuff way beyond my understanding. One pulled up beside us at the washdown and he pointed about 2 or 3 cracks .. they guy said the trailer was only a few months old but had done a few long trips.This was quite a few yrs back , things most properly (hopefully) changed a lot since then..

 On the other hand, I still check my galv chassis tyres even before a 5 min trip to the ramp..

So in retrospect doing so in my books is a positive regardless if galv or alloy.

Seen a few cracked galv trailers at the ramp also.

Don't wanna hi-jack the thread MB... Was just chucking it out there for a bit of conversation.

But yes... absolutely they are expensive. Once you have one though .... You'll never go back.

It would still be a consideration and would recommend researching the manufacturer before purchase.

Applied it tonight. Slightly messy process with at least one explosion of product in my face, but treated a standard trailer. Put it in all the holes until it was leaking out the other end (sounds so wrong!). 

Started applying CRC Soft Seal. Couldn't get the 4L bottles locally, so just spray cans 500ml. Easily got through a can. Will probably need another two. Very obviously yellow when applied. Not necessarily a bad thing because you can see what has already been covered.

Also have a can of Lanocote for fittings, but haven't got around to applying it yet. 

That should do it!  

Its the winbch drum I have found gets the most corrosion damage.

I layer up lanocoate , leave few days then load wind the riope back on every couple years.

 The rest of my winch and post is pretty clean.

 The winch bushes are about $1.75 plastic.. dont lube or get CRC petroleum products into them. They are meant to be sealed. I mix a bit of inox food grade grease and oil together and inject thru the seals with fine syringe.

If you get the noisy/ shudders on pull out...the 1st set gears/ bushes to look at is the idler gear/ shaft...inject that will sort.. dont bother with the rest for next few yrs....

The gears I keep pretty well greased up, every time I grease the motor bushes, check bearing buddies etc.

 I also have a short 2 T tie down from the bow eye hooked back over the winch. Pull boat up with winch, pull up the tie down then back the tension off the winch a little...take the load off the drum plastic bushes.

Then re check the rear engine well tie downs.. these also hold the boat forward.

This lanacote sticky thing..

I use the pot grease then diluted with old turps or kero.. this evaporate slow which means gives lot time to soak / spread into cavities cracks etc.

As to sticky, yep for a few days.. then its sort of sold sicky for a month .. then its just brown marks...

And stick rope.. you unwind the rope, slap the lanacoate in ... then wind it back up TIDY  under bit of load from out over the hitch side.

Loaded .. I used to use the old bradford with the handbrake just on...

Reason, and have no idea why it works.. when wound on tidy it has a memory and will do so everytime.

And while got the rope unwound

My rope is about 2 to 3 turns still on the spool when hook the boat at the end of the roller trailer.

I work very hard at being lazy .. I found this out.. old posts when sorting ratios weight etc to pull the Commander up with a 18v drill..

It works out that once the 1st layer is wound on the spool , the next layer is around 1/3 heavier .. next layer 3/4 nearly 2X the weight...next think was well over 2X

So hence my rope is only as long as need, makes that last 'Im sick of this  'meter"' easier...