I have a 2000 model 20’ pie rail bumper pull trailer, bought it new. It’s always been stored outside. Has the original boards, never did any preventive treatment to the boards. They are weathered, but still good.

Is the wood dry or showing any signs of cracking?

Well sure, it’s 20 years old. But not rotting, I’m in a drier climate.

Oil will make it last longer...dry rot is still rot...degradation of structural integration ….

Another vote for the oil/diesel mix, I also use it. I used to only use Oak boards in my cattle trailers and lowboy, but this pressure treated wood is not so good these days, so I went to Oak with the oil/diesel mix on my light duty flatbeds as well. I had some creosote treated utility poles cut for my lowboy, and discovered they were too soft when you drive the dozer on them, it chewed them up quick. They may be a good alternative for a light duty trailer though.

Used motor oil with a little diesel mixed in

Why does the oil have to be used?

It is free.

Good use for waste oil...you could use new with the same result...

oil and water dont mix. oil is a water repellent. if water is repelled it does not soak wood. If it does not soak wood you dont have rot. If you dont have rot the trailer bed will last longer . If the trailer bed last longer less head ache. Oh yeah , like dogcatcher said, its free.

Amazing!

Well articulated

Slightly off topic, but at the Harden Sawmill in Sanger they'll cut you custom creosote trailer floor boards out of telephone poles or RR ties. (you can supply poles/ties or they will)
Best, longest lasting trailer floor boards money can buy, and no need to bother treating them with anything.

I have an over abundance of used motor oil/hydraulic oil/diesel.

Probably 50-70 gals if anybody wants some.

When I worked as a semi-trailer mechanic and we would replace the wood floors in the trailers (most now are aluminum), we would get all the (oak) boards cut and ready, then pull one board from the center out onto the floor and turn it upside down. All the other boards were then flipped over as well in place. We rollered the (now top) side with a 50/50 mixture of creosote and diesel fuel, including the edges. It dried quick. Then flipped each of the boards over (reinserting the middle one previously pulled) and screwing them down with self tapping Torx trailer deck screws. We got 110 hours of flat rate labor to replace a floor and my working buddy and I could knock out a floor in a 10 hour (times 2) day.