With the Mac you are going to have to tow it everywhere, which can be ok depending on how you want to use the boat. We are trip type sailors with our Mac vs. day sailing and anchor in remote places and wanted the dinghy to go ashore. Unless you need to go ashore and you can beach the Mac do you need a dinghy?
We have always....
...towed the dinghy without problems except for the first trip where we just pulled her with a poly line. The dingy would run into the back of the Mac, the line would get around the outboard and rudder. It was a mess.
After that I turned the swim ladder into...
http://purplesagetradingpost.com/sumner/macgregor2/outside-30.html
...a tow bar and no more problems as it kept the dinghy secure just behind the boat and it couldn't get into anything. It is also nice to use the ladder out like that to get into and out of the dinghy and you just pull out the one brace and the ladder goes down. With the tow bar we have towed hundreds of miles including Florida's west coast and across Florida Bay. We are conservative when we travel though and if worst came to worst I'd cut the dinghy loose, but we have never had a problem (also don't tow with the outboard on).
I would not want to tow a hard shell with our boat as it would be banging into the ....
..boat at night. I also feel much safer in the Zodiac...
...in waves vs. a hard shell, but you don't row it when the wind picks up and it is a pain to row without wind so consider that. Short distances I paddle with a kayak paddle sitting on the bow. Otherwise I use the outboard and would not get one unless I had an outboard.
On the PVC deal I wouldn't let that discourage you if it is in good shape and you aren't leaving it in the water all of the time. We paid $600 for a 4 year old Zodiac 9 footer, about half new price. It is still fine after 3-4 more years of use, but we only use it for our trips, so it has only been in the sun about 5 months during that period.
We made dinghy chaps...
http://purplesagetradingpost.com/sumner/endeavour-main/canvas-14.html
..for it last year anticipating having it on the back of the Endeavour for longer trips and hoping to extend its life until we sell the boat. Since we use it on both boats we need to have a soft bottom so we can fold it up and haul it between FL and Utah. It does have a wood floor though and the keel also blows up which helps it track better in the water vs. a flat bottom.
A rib or hypalon would be great and if we were younger would probably get one, but this dinghy has worked great for us,
Sum
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