In my career I've come accross a lot of boat owners that cover their trailer and cradle
pads with carpet to protect the underside of the hull
where it rests and this may seem like good practice....not quiet.
I'm currently treating a boat for osmosis
that hasn't even seen the water
yet which is a absolute shame.
The moisture readings are low as expected throughout the hull
until you come to the areas where the boat rested on the carpeted pads, the moisture readings go through the roof and there is visual evidence of glycol blistering.
Athough the boat has never been in the water
it did sit on its trailer for some years, exposed to rain, which soaked the carpeted pads and being a lot less dense, the rainwater migrated through the gelcoat
a lot faster than that of saltwater.
For me I'll be using pads cut from old tyres which drain of water faster after a bout of rain and it's a lot easier and cheaper to deal with the black marks left behind.