I don't know what the difference is between Eternabond tape and Eternaseam but I've used Eternabond tape and like it for a more permanent solution than traditional caulking/sealants. I'm gradually working my way around my roof with the goal of being done before our rains start again here in northern California.
Given that you're in Seattle, I'd highly recommend the Eternabond or Eternaseam route.
Since your's is a TPO roof, Dicor should work but you're wise in attempting to get specific info from Winnebago. As you may know, Winnebago publishes sealant callout sheets online for motorized Winnebagos but not for towables.
2002 Itasca Suncruiser 35U