varnish, then apply aluminum???????

I'm ready to skin trailer with aluminum. Should plywood be spar varnished before applying aluminum? Will henry's 663 adhere to varnish, if it is to be applied first? 

or t n ttt for short (tnttt.com)
https://www.tnttt.com/
seahorse wrote:Thanks Mike, CPES sounds like a great product, BUT.......the price is more than my budget will allow .........Rob
seahorse wrote:Mike , your TWISTING my arm..........My question for you is........How much CPES to cover 125 sq. feet?