The UV degradation of the plastic would be my biggest concern for it. You might want to consider a stitch-and-glue wood dinghy. There are quite a few that have excellent rowing characteristics, and might be better suited for what you're doing.
When you say you're going to be gunkholing, what is the mothership vessel going to be??? That may determine what will work best for you. A Nichols NN10 might also be a good, albeit expensive, choice.
SD.. I own a Walker Bay dinghy that I have left sitting on the beach in front of our house since I purchased it back in 1998. It's been there 365 days per year for almost ten straight years and it's no worse for the wear.
A few weeks ago my neighbor came over and mentioned that it had been flipped over by one of the moon tides and was full of frozen ice. I went down to the beach with him and flipped it back over with his help. Even crashing down onto the beach, full of ice, in 15 degree weather & after 9+ straight years of UV, did not crack or damage this dinghy.
While I've never been a fan of my Walker Bay, I think it's a very poor design stability wise, I do use it as my "drag" dinghy to drag over the rocks and into the water at my home mooring. I have beat the crap out of this thing and could really care less about it seeing as I only paid $385.00 for it brand new when they first hit the market and the thing keeps on going.
That being said I have yet to find a fiberglass or inflatable that can handle the abuse my plastic Walker Bay has taken. I wore the bottom off my Puffin dinghy in two seasons dragging git up and down the beach and needed to re-glass and fair it over. On the other hand I have yet to actually have an inflatable actually last me ten years and I DO take very, very good care of them. Currently my AB 8VL is going on 4 years and actually doing quite well but time will tell.
My brother actually owns one of the first Perception Sea Lion sea kayaks to be made of roto-molded plastic and that thing is still going strong too and is about 16 years old or so & is showing no signs of age. It was on the beach with my fiberglass kayaks during the big Nor Easter and was mashed against trees by waves and had the rudder broken off but it survived! I wish I could say that for my fiberglass kayaks...
The only two boats to survive that storm on our beach were my Walker Bay and his Sea Lion...
By the way the "yellow kayak" or the one pictured upside down was kevlar!!
I have actually spent a good deal of time talking with David, the owner of Portland Pudgy, due to the fct that our booths at the Maine Boat Builders show were next to each other and it's a very, very cool and impressive design. During the show there were more owners of Pudgy's hanging around the booth and doing the selling for David that he barely had to speak. these things sell themselves and in a three day show I never once heard an owner complain about the Pudgy.
And here's a picture I just took 5 minutes ago, in the snow storm, of my Walker Bay sitting where she has been since 1998 year round!!
In short I would not worry one iota about the longevity of the plastic!