Through bolts bother me in the sense that each time you tighten them it pulls it further through the board and as some have found even using stainless they tend to spin when you are trying to remove them.
Lags on the other hand you can tighten and know they are still gripping the board and much easier to change by lifting the hull slightly and sliding the board out say during the cold months
I have 2x4's on the 2010 trailer and would probably feel better using lags if it had 2 bolts per point as when 2x6's are used
So what size boards do most have and whether they are carriage or lags???