Hello:

a. Regarding the typical Wood horizontal type of Clapboard siding:

Is it desireable to prime the backside of the planks ? Why ?

My thought being that it "might" be better to have it un-primed to allow
moisture to escape ,
but am not sure, hence the question.

b. The same question, for T1-11 wood panel type of siding.

If the answer to either is "yes" to either, is it actually available this
way ?
From which mfg(s), please ?

Thanks,
Bob