Replacing floor of OLD pickup box trailer

I got this pickup box trailer for FREE. the floor is very rotten and un-usable so I started cutting the bolt heads off and ripping it out. My question is what to replace it with. I want something wood but don't want it to swell and buckle in the middle like the old one did. I don't have a welder or heavy metal working tools to install a plate floor Primary purpose is to haul my tiller and snow blower occasionally and to haul dirt in it this spring. old deck looked maybe like 1 inch boards tounge and groove?
Could I just use 2x8 and stack them as close as I can?
What should I use and how is this normally done?

use a piece of 3/4 inch plywood

If using plywood use a lot of paint or sealer, and leave drain holes in the corners, that should make it last a bit longer.

Get a plastic pick up bed liner for it.

I would use a piece of 3/4 inch treated plywood or 1 inch. Did that on a deer stand about 20 years ago and had to replace it this past fall but hey it lasted 20 years

Replaced the floor in my 65 Chevy way back in 1980.

Used treated 2x6x8 lumber and one 2x4x8 in the middle.



Installed boards from each side towards the middle using carriage bolts.

It is strong enough to hold most anything I need to haul during my lifetime.

If you're not going to be hauling small grain or seed, fine sand- then plain boards and 1/4 inch carriage bolts will work good. 5/4 deck boards next step up and the treated deck boards will last long time. The slight gaps between boards will let water drain, keep center from bowing up. 3/4 or 1 inch exterior plywood is good also- but need to cut and notch at side or offset for a full box trailer outside fender wells- many pickup boxes were 4 foot between fender wells just for the 4x8 plywood sheet and had 1 foot space extra to side of box fore and aft of fender wells- you look like mostly external fender and 2 inch dimple to inside of box. 5/4 x6 inch by 8 deck board to outside on each side and a 2 inch wide notch at fender dimple, then fill in with deckboard or 1 inch treated plywood sheet depending on wet weather likely when setting outside. Get old boards out first, check metal for rust, use a POR/phosphoric acid primer before putting on boards. Plain boards with deck sealer or oil finish common in many places. Linseed oil, spar varnish or in lots of trailers/racks a used engine oil coat every year or two. I used oak flooring boards on last little trailer project, spar varnish and some leftover weather seal. Cypress boards on special from Menards was used on a previous trailer, brother gave it some more 10 weight last year and it is mostly inside now. RN

How about using composite decking boards that won't rot?

Look into marine plywood. I have had it in the floor of a utility trailer that sets outside about half the time for 15+ years.

Some of the chemicals in treated lumber are corrosive to metal so keep that in mind. Yellow pine was used in manure spreaders.

If you want something though, you should get some Oak 2x8s. They are getting harder to find these days, but you might have some luck at a local sawmill or mill shop. Counter sink the bolt heads and what ever you put in or take out will slide with ease. Some of the old trimmers even pour a quart of oil in the wood every once in a while to preserve the wood.

I use "elevator bolts" with plywood construction. Gives you a flat surface and doesn't pull through.

We replace all our trailer floors with 2x6 or 2x8 pine and on a hot summer days we pour as much used oil on it that it will absorb. We can haul anything that can get dirty including dirt. Fine sand might slip through but we lay a 1/4inch plywood sheet down first. The ply wood we keep on hand for a lay down when making repairs outside the shop. The plywood is used for moving stuff that can't get dirty as well

Take a look at some Advantech sub-flooring, it is strong, very water resistant and does not buckle or separate easily. Goggle it .

2X Advantech, you won't believe the warrantee.

New Floor installed. due to limitations to some welding modifications on the box I was limited to 3/4" thick lumber. Used the elevator bolts and now I will seal it with something when it warms up. Thanks for the help!