eberspacher silencer heat shield

[Tomtom39]

Dear All
I have installed a Eberspacher water heater in to my yacht for the purpose of heating. It actually works brilliantly and better than my previous air blown heater as it gets the heating further forward it to the yacht! through the hot water pipes! anyway my question
I have installed the heater in my aft lazarette which is a perfect location and is nicely out of the way!
The issue that I am having is that I installed an exhaust silencer to the eberspacher which has made a massive difference to the exhaust note and attached the bracket to my aft lazarette shelf which is wood - I installed some stainless steel L shape metal over the wood shelf and attached the silencer bracket to this but it is getting hot after running for approx 2 hours. Whilst I am sure it will be ok I would prefer to get this installed correctly. Is there something that I can install between the bracket and stainless steel plate that will stop heat transfer! maybe some heat resistant rubber bushes? I have in the past used automotive exhaust heat shield mat and that has worked.I feel in this case the heat is being transferred via the fasteners!
Any help would be appreciated