I've paddled the Nimbus Telkwa reg. for 8 years and it has been a great boat. It is well designed, stout and the craftsmanship of construction is exceptional and most importantly one can carry an amazing selection of wine. Three features I like are the recessed deck fittings, flush/bombproof hatches & an under deck neoprene "shelf" where I can store all the crap that would normally collect on the deck. It does weatherhelm in a breeze hence the rudder.
I have a knee tube in my Romany Explorer (basically what you have described, but it's a fibreglass tube suspended from the deck in the cockpit), and love it. It houses my battery pack for the GPS, a large water bottle, gloves, maybe some fishing tackle or crab bait and whatever else I want to throw in there. It keeps everything warmish and dry from spray. Everyone who's never seen a knee tube before agrees it's a great idea! Most manufacturers of fibreglass boats now offer them as an option when building a custom boat.