I expect Thompson's would be better than nothing, but I can't imagine it would add the degree of water resistance that CPES would. That resin really locks things up. Two coats of the resin (with curing time between them) and wherever it went water will not be going. I don't think the Thompson's can seal up end grain like that. It probably works okay on surface grain, but end grain is where you get your wicking issues and subsequent rot. (Note that this also applies to any holes you have made for hardware--again, end grain has been exposed and moisture will work its way in there.)