First off, let me say I do not have a stacker. We almost purchased one a few years ago when we ordered our 26' Haulmark Edge but in the end I decided against it mainly due to the weight. I was happy with the way my coach ran weighing 36k pounds and towing 8500-9000 pounds with our previous trailer and cargo. I figured 10k maybe a little more would not be a big deal but 16-18k pounds with a stacker and all my******would be way too much for my little ISL to tow and me still be happy with it. If you have the need and the power to handle 16k plus pounds of trailer and cargo being towed, I say do it. If you really don't have the need for hauling everything at once and can get by with a standard enclosed trailer I would recommend that, even if you have to go a few feet longer, in the end it will be easier loading/unloading. We haul our four door Jeep Wrangler and our HD Ultra Classic in our 26' comfortably. That is even with a workbench, toolbox and cabinets in the front.
I have a couple of friends that tow stackers and love the trailers once they are loaded and once they are on the road. They hate loading them due to the procedure and time involved. That is one aspect that I hadn't thought of when looking.
One has a 40' Diplomat with the ISL400 and tows a 30' Progressive stacker. He runs down the interstates well but the grades kill him. Another friend has a 45' Newell and tows a 24' Haulmark Edge stacker. Him and I run pretty neck and neck on the grades, maybe a slight advantage to him with his 600 hp engine but his coach also weighs around 54k pounds not towing anything.
You more than likely will have some issues in some camprgounds due to finding sites long enough. I have only been in a few where I had to unhook and park the trailer in an overflow area. Some people don't mind that but I absolutely hate it as I like to remain hooked up.
I have found this past summer that making reservations early enough in advance was the key to getting into sites long enough to not have to unhook the entire season when traveling. If you are "winging it" this may not be the case.
Last make certain your hitch is rated accordingly and if not get it reinforced to handle the kind of weight you are going to be dealing with.
Mike.
P.S. there is also several threads/discussions going on about this very topic over on IRV2.com right now as well.
2003 Monaco Dynasty/ 26' Haulmark Edge trailer
2011 Jeep Unlimited Rubicon