We didnt intentionally leave any gaps but the boards are not real tight. I think we are gonna treat the wood with some kind of sealant at a later date. The pt wood is very wet so I think we need to wait on that a bit.

i replaced my trailer deck last year i left about half inch gap between boards my reason for doing it was ease of cleaning the only things it huals regularly is my zero turn, 318 garden tractor and 4 wheeler. mud and grass fall through the big gap easier. i used treated 2x6 and they were super wet as well. i let it dry out for a good 4 months in a climate controlled shop over our cold season then i used old motor oil applied with an old paint brush i did this 2 times as i could tell where it had really sunk into the wood so added a second coat. i went super heavy on the end grains and it seems to be holding up great rain pretty much runs off it.

If you've ever seen the warehouses they store greentreated lumber, you'll see a sprinkler system used to keep it wet. When delivered to lumber yards they recommend to store in the shade and not to open up another bundle till the first one is used up or you'll end up with a pile of airplane propellers.

If ya really want them to last use that Shou Sugi Ban treatment. It is a Jap deal where you burn the wood twice with a torch and then apply about any oil to it. Lasts forever and gets real hard also. I have used it and it works great, even with pine. I did some poplar back in the eighties and it still looks like new today.

My 16 foot trailer was built in 1998. I replaced the decking 8 months ago. Luckily I am a procrastinator and had bought the material Pre-covid at normal prices. Getting ready to put a new metal roof on my one building. Bought the metal at the same time as the decking at about half of the current cost.