Or, with the current lack of enforcement these days, just use the darn thing until you get pulled over. Which at this rate will be never. And they'll probably just give you a warning. I get doing things by the book to be legal, but I see so many people with expired tabs these days. It's a joke right now. Yeah, I'll probably renew my boat, trailer & all 3 cars, but man it seems useless these days.
Funny story- I saw a car with both a 23 tab and a 24 tab. Yep, they put the new 24 tab over the month tab. Haha. And yes, it was a white Subaru.
Years ago, I bought a 12' aluminum boat from a kid and the trailer was home built by him and his grandfather. Cool grandpa! Well, I took it to the WSP inspection (lots of them available back then) and they told me to put fenders on it. I put fenders on it and it passed easily. Your trailer will pass with flying colors as long as the lights work.
If you're not on the Columbia or Puget Sound I doubt anyone will check the boat tags. When was the last time anyone had their boat tags checked? And by who? The only place it might happen to me is Lake Tapps. Pierce County Sheriff actually patrols that pretty hard since there are so many dumbasses there.
I fish Puget Sound and Hood Canal with my boat and have never been checked. Will I renew my tabs in June?? Probably only because of Tapps.
Good luck! Nice boat!