FWIW: I purchased a new Keystone fifth wheel from Camping World in March, 2013. Prior to taking delivery, I had CW remove the factory junk STs and install Firestone Transforce HT 235/85R/16 LTs.
One would think that if installing LTs on a brand new 12,000 lb trailer that is designed for STs (per the manufacturer sticker on the trailer)was unsafe or voided any warranties, Camping World would not have installed them. Or at least they would have had my sign a disclaimer.
I love the LTs. They are a by far a superior tire than any ST tire I have owned.