http://www.simplicityboats.com/jointtest.html

Roger,
These are joint tests on plywood, not a backing plate on vinylester
glass so it's not apples and apples, but it is knowledge... My belief
is that the 5200 will work just fine for your knotlog backpalte given
the low psi load that will be put on it... I would not hesitate to use
the 5200 for what you are doing..

denny