Is this a good deal for a used 2016 sun seeker 3050?

You might find that new ones are under $70K. We were at a dealer open house last month, and the new Sunseekers were in the upper 60s. Get a quote from rvdirect.com just to see what the typical low price is for new. (You should then be able to find a dealer in your region who will match it, if you want to buy new.)
If the 2016 is built on a 2015 chassis, which is typical, then you will be getting the 5 speed trans instead of the 6 speed which started with the 2016 chassis. For me, I'd definitely want the 6 speed if I was buying almost new. A lot of owners don't like the shift pattern of the 5 speed.

I'd go for 5 years old. I think the price is rather high for the unit you are looking at.

With that many miles it was likely a dealer rental unit. Might not be an issue but could be.